Open Source Slack Alternatives

Rocket.Chat is an open source communication platform built for organizations that can't hand their data to a third-party cloud. It brings together real-time messaging, voice and video calls, screen sharing, and AI-assisted workflows into a single environment you host and control entirely.

Security is central to the design. It supports on-premises, air-gapped, and secure cloud deployments, and has been used on classified U.S. government networks including NIPRNet, SIPRNet, and JWICS. It holds DoD Authorization to Operate (ATO) up to Impact Level 6. Few commercial team chat tools come close to that clearance level.

Beyond defense and intelligence, it fits any organization where data sovereignty matters: government agencies, critical infrastructure operators, financial institutions, and enterprises subject to strict regulatory requirements. The Swedish Electrical Safety Board and EU agency eu-LISA both use it for secure internal and cross-organizational collaboration.

Core capabilities include fully encrypted conversations, granular access controls, fine-grained data retention policies, and comprehensive audit logs. Federated communication lets teams coordinate across organizational or jurisdictional boundaries without routing data through external services.

The architecture is extensible. Teams can install pre-built apps or build custom integrations to fit specific workflows, without being locked into a vendor's roadmap. If you want something lighter, Mattermost is a comparable self-hosted option worth considering. The built-in AI features handle routine tasks and surface relevant information during active conversations — for teams that want a standalone AI layer instead, LLMChat takes a different approach.

Mattermost is an open-source collaboration platform built for organizations that require high levels of privacy, security and control over their communications. Some key features and benefits include:

• Flexible deployment options: Can be self-hosted on-premises, in private clouds, or air-gapped environments
• Advanced security and compliance: Built-in access controls, audit logging, and data retention policies
• Customizable and extensible: Open APIs and integrations to connect with existing tools and workflows
• Channels for team communication: Secure messaging, file sharing, voice/video calls
• Playbooks for process management: Checklist-based workflows to standardize repeatable processes
• AI-powered features: Ability to integrate AI capabilities while maintaining full data control
• Mobile and desktop apps: Access from any device with native mobile apps

Mattermost is designed for industries like defense, government, financial services, and critical infrastructure that have stringent requirements around data sovereignty and security. It provides a self-hosted alternative to cloud-based tools, giving organizations complete control over their collaboration environment.

The platform aims to improve team productivity and accelerate mission-critical work by providing a centralized hub for communication, process management, and integrations. With its focus on security and flexibility, Mattermost enables organizations to collaborate effectively even in highly regulated or air-gapped environments.

Nextcloud is an open source, self-hosted file sync and share platform that allows organizations to store, share and collaborate on files securely.

Key features include:

• File sync and sharing across devices
• Real-time document collaboration
• Video calls and chat
• Calendar, contacts and email integration
• Advanced security and access control
• On-premises hosting for full data control
• Customizable and extensible through apps

Nextcloud is designed for organizations that need secure file sharing and collaboration while maintaining control over their data. It can be deployed on-premises or with a trusted cloud provider.

Some key benefits of Nextcloud:

• Improved productivity through integrated collaboration tools
• Enhanced security with end-to-end encryption and granular permissions
• Compliance with data protection regulations like GDPR
• Lower costs compared to proprietary cloud solutions
• Flexibility to customize and extend functionality

Nextcloud is used by thousands of organizations worldwide, including major enterprises, educational institutions and government agencies. It provides a powerful yet easy-to-use platform for secure content collaboration.

Zulip is a powerful, open-source team chat application designed to revolutionize how distributed teams communicate. Unlike traditional chat tools that can feel chaotic and stressful, Zulip's unique threading model organizes conversations by topic, making it easy to manage multiple workstreams and stay on top of important discussions.

Key features and benefits:

1. Threaded Conversations: Zulip's core feature is its topic-based threading, which allows teams to have multiple conversations simultaneously without losing context or creating confusion.

2. Efficient Communication: The organized structure helps team members quickly catch up on relevant discussions and reduces information overload.

3. Flexible Deployment: Choose between Zulip Cloud for convenience or self-host the 100% open-source software for ultimate control and compliance.

4. Cross-Platform Support: Access Zulip from desktop and mobile apps, ensuring seamless communication across devices.

5. Rich Integrations: Connect Zulip with your favorite tools and services to streamline workflows.

6. Powerful Search: Easily find past conversations and shared knowledge with Zulip's robust search functionality.

7. Open Source: Benefit from a transparent, community-driven development process and the ability to customize the platform to your needs.

Zulip is ideal for various use cases:

• Businesses: From small startups to large enterprises, Zulip helps teams manage projects and communicate more effectively.
• Education and Research: Universities and research groups use Zulip to facilitate collaboration across departments and continents.
• Open Source Projects: Many open-source communities rely on Zulip to engage contributors and make faster decisions.
• Events and Conferences: Organizers use Zulip to create interactive spaces for attendees before, during, and after events.

With its focus on organized communication, Zulip empowers teams to work more efficiently, make decisions faster, and create a searchable knowledge repository as a natural byproduct of their conversations. Whether you're managing a small team or coordinating thousands of contributors, Zulip provides the structure and flexibility needed to succeed in today's distributed work environment.

Huly brings together the tools that most teams spread across four or five separate apps. Project management, real-time chat, collaborative documents, and a virtual office all live in one workspace. It's built for product and engineering teams who are tired of context-switching between a task tracker, a Slack alternative, and a Notion alternative.

The project management side covers what you'd expect from a modern tracker:

• Team Planner consolidates individual tasks into a shared calendar so you can see workload across the whole team at a glance.
• Time-blocking lets you turn tasks into structured time slots in your personal planner.
• GitHub sync works both ways. Huly connects to GitHub Issues and GitHub Projects, syncing changes instantly, supporting multiple repositories, and migrating milestones between them.
• Advanced filtering makes it practical to search and slice project data across large backlogs.

The virtual office is a built-in audio and video conferencing environment. Teams can create custom rooms for departments or recurring meetings, and invite guests without sending them to a separate tool. No third-party conferencing app required.

Documents in Huly support rich text, images, attachments, and code blocks. Live real-time collaboration means multiple people can edit simultaneously. You can tag teammates, link directly to issues, and assign action items from within a document, which keeps planning and execution connected. Version history tracks every edit.

The collaborative workspace also includes a unified inbox and instant notifications, so updates from tasks, documents, and chats surface in one place rather than scattered across tools.

Huly is self-hostable, which matters for teams with data residency requirements or those who simply want control over their infrastructure.

Element is a powerful, open-source communication platform that puts privacy and security at the forefront. Built on the decentralized Matrix protocol, Element offers a comprehensive suite of features for both personal and professional use.

Key benefits of Element include:

• End-to-end encryption: Ensure your messages, calls, and shared files remain private and secure.
• Decentralized architecture: Choose your own server or self-host for complete control over your data.
• Cross-platform compatibility: Seamlessly sync conversations across desktop, web, iOS, and Android devices.
• Rich collaboration tools: Enjoy group chats, voice and video calls, file sharing, and integrations with popular productivity apps.
• Interoperability: Connect with users on other Matrix-based platforms, fostering open communication.
• Customization options: Tailor the interface and features to meet your specific needs or brand requirements.
• Community-driven development: Benefit from continuous improvements and innovations from a global developer community.

Whether you're an individual seeking secure messaging or an organization looking for a flexible, scalable communication solution, Element provides the tools you need to stay connected while maintaining control over your data and privacy.

Fluxer is a comprehensive communication platform that prioritizes user privacy and community building. This free and open-source messaging app offers everything you need to connect with friends, organize groups, and build thriving communities.

Core Features:

• Full messaging suite with Markdown support, private DMs, group chats, and organized channels
• Voice and video calls with screen sharing, noise suppression, and multi-device support
• Advanced moderation tools including granular permissions, audit logs, and webhook support
• Powerful search with message history filtering and quick switcher functionality

Customization & Control:

• Upload custom emojis and stickers to personalize your experience
• Apply custom CSS themes and display options for a tailored interface
• Self-hosting capabilities - run your own instance with full control over your data
• Switch between multiple instances seamlessly

Built for Privacy: Made in Sweden with a focus on transparency, Fluxer is fully open source under AGPLv3 license. The platform supports responsible disclosure through their security bug bounty program and maintains active community involvement through their beta program.

Perfect for individuals seeking Discord alternatives, communities wanting data sovereignty, or organizations requiring secure, customizable communication solutions.

Break free from endless subscription fees with this self-hosted group chat solution that puts you in complete control. If you've used Slack or Teams, you already know how to use Campfire - but without the monthly charges that never end.

Key features include:

• @mentions and direct messages for seamless team communication
• Mobile web support with PWA capabilities and push notifications
• Private and public rooms with clear visual indicators for unread messages
• Search functionality with saved searches for easy access
• Dark mode support for comfortable viewing
• Chatbot API for custom integrations

Perfect for multiple use cases:

• Replace expensive chat subscriptions as your primary communication tool
• Create backup chat systems for when other services go down
• Establish private executive spaces or board communications
• Set up temporary chat rooms for conferences and events
• Use as educational material to study high-quality code

Technical advantages:

• Runs on your own hardware, cloud services, or hosting providers
• Automatic SSL certificate setup during installation
• One-command Docker deployment
• Automatic updates (can be disabled for manual control)
• Works on air-gapped networks for high-security environments
• Scales from 250 to 10,000+ concurrent users

You get the complete Rails source code, allowing full customization for your specific needs. One-time purchase, no recurring fees - own your chat system and your data forever.

Colanode is a comprehensive collaboration platform that brings together all the tools your team needs in one self-hosted solution. Unlike traditional cloud-based alternatives, this local-first application gives you complete control over your data while providing instant access to your content.

Key features include:

• Real-time chat for seamless team communication
• Collaborative document editing with flexible formatting options
• Built-in file manager for easy file sharing and organization
• Offline support that syncs when you're back online
• AI assistant to help with content creation and workflow optimization
• Zero loading times thanks to local-first architecture

The platform is designed for teams who value data ownership and privacy while maintaining the collaborative features found in popular tools like Slack and Notion. With self-hosting capabilities, you can deploy Colanode on your own infrastructure, ensuring sensitive information never leaves your control.

Whether you're managing projects, writing documentation, or coordinating with team members, Colanode provides a unified workspace that works both online and offline, making it ideal for distributed teams and organizations with strict data governance requirements.

Cinny is an open-source Matrix client that provides a secure and elegant interface for seamless conversations. Built on the Matrix protocol, it offers:

• End-to-end encryption for enhanced privacy and security
• A clean and intuitive user interface for effortless navigation
• Organized conversations, separating DMs from channels
• Adaptive input that adjusts to your actions without disrupting your workflow
• Calm visual design with proper alignment and formatting

Cinny is constantly evolving to create a better communication experience. As an open-source project, it benefits from community contributions and transparency.

Key features:

• Simple and elegant interface
• End-to-end encryption
• Organized conversation management
• Adaptive input system
• Calm visual design
• Open-source development

Whether you're looking for a secure messaging solution for personal use or team collaboration, Cinny offers a refreshing alternative to traditional chat applications. Experience the power of open-source, decentralized communication with Cinny's user-friendly approach to Matrix.

Stoat (formerly Revolt) is a group chat app built for friends and communities who want the features of mainstream platforms without the surveillance business model behind them. It's a direct Discord alternative that covers the basics well: servers, channels, voice chat, file sharing, and markdown support, all without ads or data collection.

Built in Europe under EU data protection law, the codebase is public and the privacy policy is short enough to actually read. There's no investor pressure shaping product decisions, which means features exist because users want them, not because they serve an ad-targeting pipeline.

A few things stand out from the typical chat app:

• Custom emojis and animated avatars are free, with no subscription tier required
• Group DMs support up to 50 members and work with bots, making them useful for project collaboration or ad-hoc voice groups
• Role-based permissions and moderation tools handle communities of any size, from a handful of friends to thousands of members
• Theming ships with built-in options, community themes via a Discover section, and custom CSS for those who want full control
• Cross-platform sync covers Windows, macOS, Linux, Android, iOS, and the web
• Self-hosting is supported if you want full control over your own instance
• A public API powers the official apps themselves, so third-party bots and custom clients are first-class citizens

Compared to tools like Rocket.Chat or Twake Chat, Stoat leans toward the consumer end: it's designed to feel familiar to anyone coming from mainstream chat apps, with a lighter footprint and fewer enterprise-focused features. The 20MB file upload limit and server-specific profile pictures are available without paying, which removes friction that similar platforms put behind paywalls.

The issue tracker is public and the team runs a community server, so feedback has a direct path to the people building it.

Wire delivers military-grade security without sacrificing user experience. The platform features always-on end-to-end encryption for messages, files, and calls, while maintaining an intuitive interface for seamless team collaboration.

Key capabilities include:

• Instant messaging, file sharing, and video meetings with invisible security
• Flexible collaboration tools for internal teams and external partners
• Complete data sovereignty with on-premises deployment options
• Enterprise features like SSO, SCIM, and granular admin controls

Trusted by industry leaders including BMW, ExxonMobil, and government organizations worldwide, Wire ensures your sensitive communications remain private and compliant. The platform is particularly valuable for organizations requiring:

• Zero-knowledge encryption
• Regulatory compliance
• Digital sovereignty
• Scalable secure collaboration

Mezon is a comprehensive community platform designed for gamers and social enthusiasts who want to create their own digital hangout spaces. Whether you're looking to organize gaming sessions, chat with friends, or build a thriving community, Mezon provides all the tools you need.

The platform allows you to create fully customized spaces tailored to your group's interests and needs. You can set up dedicated channels for different games, topics, or activities, making it easy to keep conversations organized and engaging.

Key features include:

• Custom community spaces with personalized layouts and themes
• Multi-purpose chat channels for text, voice, and multimedia sharing
• Gaming-focused tools to coordinate gameplay and tournaments
• Global connectivity to meet and interact with people worldwide
• Flexible privacy settings to control who can join your communities

Perfect for gaming clans, hobby groups, study communities, or casual friend circles, Mezon adapts to any social dynamic. The platform makes it simple to invite friends, discover new communities, and maintain active engagement through intuitive design and robust communication features.

A community-driven communication platform that prioritizes transparency, flexibility, and user privacy. Built entirely by volunteers without corporate funding, this open-source solution offers a refreshing alternative to traditional chat platforms.

Key features include:

• Multi-window chat system - Chat across multiple channels and communities simultaneously with advanced window management
• Integrated economy system - Reward community members and create engaging experiences
• Customizable item system - Show achievements and enhance user immersion
• Blazor & WebAssembly technology - Superior performance without resource-heavy Electron framework
• Node-based backend - Optimized for large communities without sacrificing core features

Privacy and transparency are at the core of this platform. Your data will never be sold, and the entire codebase is open for public inspection. The community-driven development approach ensures features are built for real user needs rather than corporate interests.

Perfect for communities seeking a modern, fast, and ethical communication platform that puts users first.

Secure and private by design, Twake Chat leverages the Matrix protocol for decentralized communication that puts you in control. This free and open source messenger delivers enterprise-grade security with end-to-end encryption while maintaining simplicity for both work and personal use.

Key features that set Twake Chat apart:

• Multi-platform bridges - Connect with contacts across Telegram, Discord, Signal, and 30+ other networks through a single interface
• Flexible deployment - Use cloud-hosted or deploy on-premise for maximum data control and privacy
• Cross-device synchronization - Access your conversations seamlessly across tablets, smartphones, and laptops
• Multi-account support - Switch between personal and work accounts within one unified interface
• Corporate integration - Connect with contacts from phone books and corporate directories via SSO
• Jitsi video integration - Built-in quality videoconferencing capabilities

Perfect for professional teams who need secure communication without compromising on functionality. The Matrix protocol ensures your data remains decentralized rather than controlled by a single entity, while customizable security levels let you add extra encryption when needed.

Whether you're managing team collaboration or need a reliable messaging solution that respects privacy, Twake Chat provides the security and flexibility modern organizations require.

SAMA is a powerful open source chat server designed for modern mobile and web applications. It offers enterprise-grade security with built-in end-to-end encryption and seamless scalability through out-of-the-box clustering support.

Key features include:

• Advanced messaging capabilities including private/group chats, typing indicators, read receipts, and file attachments
• Robust user management with authorization, profile editing, user search and blocking
• Multi-device support allowing users to stay connected across devices with flexible message delivery
• Real-time presence tracking to monitor online/offline status
• Push notification support for APNS/FCM/Web to reach offline users
• Built for scale with clustering support for handling large user bases

The platform comes with a modern frontend client, clustering-enabled backend, admin dashboard, and comprehensive API documentation - everything needed to build secure and scalable chat applications.