The best open source alternative to Filestash is Spacedrive. If that doesn't suit you, we've compiled a ranked list of other open source Filestash alternatives to help you find a suitable replacement. Other interesting open source alternatives to Filestash are: Nextcloud and Firefiles.
Filestash alternatives are mainly Cloud File Sync & Share Tools but may also be File Management Utilities or Distributed Storage Tools. Browse these if you want a narrower list of alternatives or looking for a specific functionality of Filestash.
A cross-platform file manager that unifies your devices into a seamless, organized digital workspace.

Important: Development paused due to funding constraints (source).
Spacedrive revolutionizes file management by creating a virtual distributed filesystem across all your devices. This open-source application offers a unified interface to access, organize, and manage your files, regardless of their physical location.
Key benefits of Spacedrive include:
Spacedrive empowers you to take control of your digital assets, providing a seamless experience across all your devices and storage solutions. Whether you're a creative professional managing large media libraries, a developer organizing code repositories, or simply someone looking to declutter their digital life, Spacedrive offers the tools you need to create a more efficient and organized digital workspace.
Looking for open source alternatives to other popular services? Check out other posts in the alternatives series and openalternative.co, a directory of open source software with filters for tags and alternatives for easy browsing and discovery.
Nextcloud offers on-premises file sync, sharing and collaboration platform with advanced security and privacy features.

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:
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:
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.
Firefiles is an open-source alternative to Dropbox that lets you manage files across multiple cloud storage providers through a single interface.

Firefiles revolutionizes cloud storage management by offering a unified platform for all your storage needs. Here's what makes Firefiles stand out:
Multi-Provider Support: Seamlessly integrate with popular cloud storage providers like Firebase, AWS, Digital Ocean, Backblaze, and more.
Open Source: Fully open-sourced on GitHub, ensuring transparency and community-driven development.
Enhanced Security: Offers superior security and privacy compared to traditional cloud storage solutions.
User-Friendly Interface:
Efficient File Management:
Customizable: Set up your cloud drive with the backend of your choice.
Team Collaboration: Invite team members to your cloud drives (coming soon).
Cross-Platform: Available for MacOS, Windows, and Linux.
Firefiles is designed to be the last cloud storage solution you'll ever need, combining the flexibility of multiple providers with the simplicity of a single, user-friendly interface. Whether you're an individual user or part of a team, Firefiles offers a seamless experience for all your file storage and management needs.