The best open source alternative to Plex is Jellyfin. If that doesn't suit you, we've compiled a ranked list of other open source Plex alternatives to help you find a suitable replacement.
Plex alternatives are mainly Media Servers. Browse these if you want a narrower list of alternatives or looking for a specific functionality of Plex.
Free, open source media server that lets you collect, manage, and stream your personal library to any device, with no fees, tracking, or vendor lock-in.

Jellyfin is a volunteer-built, self-hosted media server that gives you full control over your personal media library. It runs on your own hardware and streams to virtually any device, with no subscription fees, no tracking, and no company deciding what you can watch or how.
The core use case is organizing and streaming media you already own. Movies are presented with artwork and metadata, TV shows are sorted by season automatically, and music is organized by artist and playlist. Beyond video and audio, Jellyfin also handles books, comics, magazines, and photos, making it a single place to manage most personal media types.
Live TV and DVR support lets you watch broadcast television and schedule automatic recordings directly through Jellyfin, which expands what the server can do beyond a static library. SyncPlay allows multiple users to watch the same content in sync, useful for remote movie nights with friends or family.
Clients are available across a wide range of platforms through both official and third-party apps, so your library travels with you. The web interface is the primary access point, but dedicated apps extend playback to phones, TVs, and other devices.
Jellyfin is licensed under the GNU GPL, meaning the source is open and any modifications must remain open under the same terms. No paid tiers. No hidden costs. No central servers collecting usage data. The project is funded entirely by user donations and run by volunteers.
It's a direct alternative to services like Plex or Emby, both of which have moved toward subscription models or proprietary features. Jellyfin's entire feature set is available without paying anything, to anyone, including commercial use. If you want a dedicated music server alongside it, Navidrome pairs well for audio-only streaming.