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.
By the way, in case it isn't obvious, you can scroll down past the video stream to see more info and links.
Also, the main OwnCast website is at https://owncast.online and you can follow the project at @owncast