Years back, the most common Plex implementation was to attach a home theater PC (HTPC) to a TV to stream media. With the proliferation of cheap streaming devices like the Chromecast, Apple TV, and Fire TV, almost no one bothers with HTPCs anymore. Thus, Plex is retiring the TV interface with the launch of its new desktop app. This will, no doubt, upset some Plex fans nonetheless.
Jellyfin is a personal media server. The Jellyfin project was started as a result of Emby’s decision to take their code closed-source, as well as various philosophical differences with the core developers. Jellyfin seeks to be the free software alternative to Emby and Plex to provide media management and streaming from a dedicated server to end-user devices.
TRITON is a media pipeline that aims to go one step further than services like Jellyfin and Plex provide. Media is fetched from a magnitude of supported protocols (HTTP, S3-compatible, Usenet, etc), converted into multiple different quality levels, and then uploaded to a S3-compatible storage provider. This enables cheap storage and ensures that buffering is never a problem.
Lots more research is needed, including a look at what others are doing with the Plex announcement. Although I did find Ampache and Airsonic which could be useful for my mixcloud issues. Imagine if they were federated too?