Open Source Projects using Java
A curated collection of the 94 best open source software using Java. Find the most popular and trending open source projects to learn from, contribute to, or use in your own projects.
Secure, customizable authentication for your applications
Stars
15,339Last commit
3 days agoLicense
Unknown
Open-source authentication solution offering flexible, self-hosted user management with advanced features and easy integration.
Open Source Alternative to:
Client-side encryption for your cloud files
Stars
16,388Last commit
9 hours agoLicense
GPL-3.0
Encrypts files and filenames locally before they reach Dropbox, Google Drive, OneDrive, or any other cloud, so only you hold the key.
Open Source Alternative to:
Centralize, transform, and stash your data
Stars
14,971Last commit
16 hours agoLicense
Unknown
Logstash is a free and open server-side data processing pipeline that ingests data from multiple sources, transforms it, and sends it to your desired destination.
Open Source Alternative to:
Real-time analytics database for sub-second OLAP queries
Stars
14,091Last commit
4 hours agoLicense
Apache-2.0
Columnar, time-indexed analytics database built for streaming and batch data at scale, handling billions to trillions of rows with millisecond query response times.
Open Source Alternative to:
Privacy-first email app for Android, no ads ever
Stars
14,166Last commit
19 hours agoLicense
Apache-2.0
Android email client from the Thunderbird project with unified inbox, multiple account support, OpenPGP encryption, and no ads or data tracking.
Open Source Alternative to:
AI-powered grammar checker for 30+ languages
Stars
15,219Last commit
10 hours agoLicense
LGPL-2.1
Check grammar, punctuation, and spelling errors instantly with AI-powered technology. Supports 30+ languages with browser extensions and desktop apps.
Open Source Alternative to:
The personal finance app for everyone
Stars
Stars growing over the last 30 days10,732Last commit
6 hours agoLicense
AGPL-3.0
An all-in-one personal finance platform. Track, optimize, grow, and manage your money through every stage of life.
Open Source Alternative to:
Realtime client-side database for collaborative apps
Stars
10,565Last commit
12 days agoLicense
Apache-2.0
Instant is a database solution for building real-time and offline-enabled applications, simplifying the development of collaborative products.
Open Source Alternative to:
2FA token manager for Android with encrypted vault
Stars
13,421Last commit
2 months agoLicense
GPL-3.0
Android app for managing two-factor authentication tokens with encrypted storage, biometric unlock, flexible backups, and import/export from major 2FA apps.
Open Source Alternative to:
Lightning-fast open source search engine for big data
Stars
12,073Last commit
8 hours agoLicense
GPL-3.0
Open source search database delivering 2.83x faster performance than Elasticsearch. Features vector search, SQL interface, and full-text capabilities.
Open Source Alternative to:
On-the-fly image resizing and conversion for your own server
Stars
11,163Last commit
4 days agoLicense
Apache-2.0
Self-hosted image processing server that resizes, converts, and optimizes images on demand via URL parameters, with built-in security against common attack vectors.
Open Source Alternative to:
Professional digital painting made accessible to everyone
Stars
10,669Last commit
8 hours agoLicense
GPL-3.0
Free and open source painting program built by artists for artists. Features professional brushes, layers, animation tools, and drawing assistants for all skill levels.
Open Source Alternative to:
Real-time observability for modern web applications
Stars
9,385Last commit
7 days agoLicense
Apache-2.0
Comprehensive monitoring solution offering error tracking, session replay, and performance insights for seamless debugging and optimization.
Open Source Alternative to:
Security-first diagramming with no login required
Stars
Stars growing over the last 30 days9,090Last commit
7 days agoLicense
Apache-2.0
Create professional diagrams online or offline with security-first approach. No registration needed. Works with Google Drive, SharePoint, Atlassian, and more.
Open Source Alternative to:
Simplify expense management for businesses of all sizes
Stars
5,082Last commit
3 hours agoLicense
MIT
Automate expense reporting, reimbursements, and corporate card management with real-time data sync and powerful integrations.
Secure email, calendar and contacts with end-to-end encryption
Stars
8,069Last commit
7 hours agoLicense
GPL-3.0
Tuta offers encrypted email, calendar and contacts with quantum-resistant security, protecting your privacy without ads or tracking.
Open Source Alternative to:
Time-series database built for industrial IoT workloads
Stars
6,426Last commit
13 hours agoLicense
Apache-2.0
Apache IoTDB manages industrial IoT time-series data with high-throughput read/write, edge-cloud sync, ultra-high compression, and integrations with Hadoop, Spark, Flink, and Grafana.
Open Source Alternative to:
Sync and transform data from any source to any destination
Stars
6,547Last commit
5 hours agoLicense
MPL-2.0
CloudQuery is an open-source ELT platform that enables easy data integration from hundreds of cloud and security tools to any destination.
Open Source Alternative to:
Enterprise monitoring for networks, apps, and infrastructure
Stars
6,525Last commit
4 hours agoLicense
AGPL-3.0
Monitors networks, servers, cloud services, IoT, and OT environments with no per-device licensing fees, available self-hosted or as a managed SaaS platform.
Open Source Alternative to:
Distributed OLAP database for real-time analytics at scale
Stars
6,169Last commit
3 hours agoLicense
Apache-2.0
Sub-second SQL queries on fresh streaming data at petabyte scale, built for high-concurrency user-facing apps and AI agent backends.
Open Source Alternative to:
Secure, encrypted notes for your digital life
Stars
6,690Last commit
19 hours agoLicense
AGPL-3.0
Cross-platform note-taking app with end-to-end encryption, offline access, and powerful organization features for privacy-conscious users.
Open Source Alternative to:
Build scalable authorization in minutes, not months
Stars
5,968Last commit
8 days agoLicense
AGPL-3.0
Open-source authorization service for implementing fine-grained access controls. Centralized, scalable solution supporting RBAC, ABAC and ReBAC with Google Zanzibar-inspired architecture.
Open Source Alternative to:
Navigate anywhere with detailed offline maps and GPS
Stars
6,116Last commit
6 hours agoLicense
Unknown
Comprehensive offline navigation app with detailed maps, turn-by-turn guidance, and specialized routing for hiking, cycling, and walking worldwide.
Open Source Alternative to:
Secure, policy-based access control for modern applications
Stars
4,638Last commit
2 days agoLicense
Apache-2.0
A scalable authorization layer that provides fine-grained access control through externalized policies, enabling secure and flexible permissions management.
Open Source Alternative to:
Free office suite with Microsoft compatibility
Stars
Stars growing over the last 30 days4,583Last commit
5 hours agoLicense
GPL-3.0
Complete free office suite compatible with Microsoft formats (.doc, .docx, .xls, .xlsx, .ppt, .pptx). Open source alternative with regular updates.
Open Source Alternative to:
Scalable SQL database for real-time analytics
Stars
4,449Last commit
17 hours agoLicense
Apache-2.0
Distributed SQL database designed for high-speed ingestion and complex queries on massive datasets, ideal for IoT and time-series data.
Open Source Alternative to:
Open-source code security engine for developers
Stars
Stars growing over the last 30 days3,264Last commit
4 hours agoLicense
LGPL-2.1
Opengrep is a community-driven fork of SemgrepCE, providing accessible static code analysis and security scanning for developers.
Open-source document editing suite for secure collaboration
Stars
3,384Last commit
4 days agoLicense
Unknown
Powerful online document editor with Microsoft Office compatibility. Integrate into your infrastructure or use trusted hosting partners for secure team collaboration.
Open Source Alternative to:
Webhook delivery platform with retries, security, and a portal
Stars
3,472Last commit
4 hours agoLicense
MIT
Add customer-facing webhooks to your product without building the infrastructure. Handles retries, signatures, multi-tenancy, filtering, and monitoring at scale.
Open Source Alternative to:
Serverless team chat over Tor, no phone number needed
Stars
2,659Last commit
3 days agoLicense
GPL-3.0
Quiet is a peer-to-peer messaging app that syncs messages directly between devices over Tor, with no central server, no phone number required, and no metadata leaks.
Open Source Alternative to:
Business rules engine with AI, visual flows, and audit trails
Stars
Stars growing over the last 30 days2,101Last commit
3 days agoLicense
MIT
Model business logic in decision tables, visual flows, and natural-language rules. Change rules without deploys, test every path, and run the same engine anywhere.
Open Source Alternative to:
Real-time stream processing made simple and affordable
Stars
2,277Last commit
22 hours agoLicense
Apache-2.0
Timeplus is a lightweight, powerful, and cost-efficient stream processing platform for real-time analytics, deployed as a single binary.
Create custom spaces to chat, game, and connect globally
Stars
2,010Last commit
12 hours agoLicense
MIT
Build your own community space for gaming, chatting, and hanging out with friends worldwide. Customize your environment for the perfect social experience.
Open Source Alternative to:
Secure, private, and decentralized file storage
Stars
2,544Last commit
4 hours agoLicense
AGPL-3.0
A peer-to-peer encrypted filesystem for secure file storage, sharing, and collaboration with end-to-end encryption and user-controlled data.
Open Source Alternative to:
Track your TV shows and movies on Android
Stars
2,171Last commit
15 days agoLicense
Unknown
Android app for tracking TV shows and movies you're watching, have watched, or plan to watch, powered by TMDb data.
Open Source Alternative to:
Local-first 2FA authenticator and password manager
Stars
1,559Last commit
11 days agoLicense
GPL-3.0
Open-source authenticator and password manager that stores 2FA tokens and passwords locally on your device, with zero-knowledge encryption and no account required.
Open Source Alternative to:
Open-source knowledge management and collaboration platform
Stars
1,328Last commit
4 hours agoLicense
LGPL-2.1
XWiki is a flexible, feature-rich wiki software that helps organizations structure and share knowledge efficiently.
Open Source Alternative to:
Unify APIs, databases, and services effortlessly
Stars
1,284Last commit
4 hours agoLicense
Apache-2.0
A powerful backend framework that simplifies API integration, enhances security, and boosts developer productivity for modern web applications.
Open Source Alternative to:
Message your coding agents as bots from any device
Stars
Stars growing quickly over the last 30 days1,017Last commit
5 hours agoLicense
Apache-2.0
Run Claude Code, Codex, Cursor, and 40+ AI agents as persistent bots across iPhone, Mac, Windows, and Linux with group chats, approvals, and end-to-end encryption.
Open Source Alternative to:
Track TV shows and movies, synced with Trakt.tv
Stars
1,469Last commit
2 days agoLicense
GPL-3.0
Android and iOS app for tracking TV shows and movies, managing watchlists, and syncing viewing history with Trakt.tv across devices.
Open Source Alternative to:
One self-hosted binary replaces Vercel, Sentry, and analytics tools
Stars
Stars growing over the last 30 days882Last commit
4 hours agoLicense
Apache-2.0
Self-hosted platform for small dev teams combining deployments, error tracking, analytics, session replay, uptime monitoring, and managed databases in one dashboard.
Open Source Alternative to:
Build AI agents and automate complex workflows seamlessly
Stars
Stars growing over the last 30 days1,051Last commit
3 hours agoLicense
Apache-2.0
Create intelligent automation workflows combining AI agents with your favorite apps and services. Connect, automate, and scale your operations without complex coding.
Open Source Alternative to:
Bright Data – Web data for AI agents and apps. Built-in unblocking, proxies, and ready-made APIs.
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