Jellyfin is an open source fork of Emby. I've been trying it out after the Plex mobile app "forgot" I paid for it, and will be migrating over soon. I haven't used Emby so I can't speak to the differences, but it seems to work very well. In some ways it's even better than Plex- turning on subtitles doesn't seem to hit performance as hard

And Jellyfin is the open-source fork, since Emby went closed-source.

I need to do more research on that. The people behind Emby seem to understand and are trying to minimize the blow-out by making 'as many features in stand alone open source modules as possible'.