The free open source livestreaming platform OwnCast has set up a demo server at:
It currently runs a loop of videos by people who self-host their livestreams using OwnCast, along with short videos promoting other libre projects.
If you run a free open project and have a short video (under 1 minute), you can have it added to this loop by contacting @owncast.
OwnCast servers include Fediverse compatibility, so you can follow them from Mastodon etc. When a stream you follow goes live, you'll see a message telling you about it in your timeline.