It has been 8 months since I made the first commit for Owncast Sentry, a bot to receive proactive @matrix notifications when @owncast instances go live. I created the bot after I found other solutions to be too slow to send me notifications. As a result, I would end up tuning in to my favorite streams well after they've already started.
Since publicly launching, Owncast Sentry has grown to be monitor 82 unique Owncast instances across the fediverse, sending notifications in 6 unique Matrix rooms. The vast majority of the subscriptions are in @ozoned's Matrix space in his RUN channel, which acts as an unofficially official fire hose of when many Owncast instances go live.
If you want to receive Matrix notifications when your favorite Owncast instances go live, Owncast Sentry might be just what you're looking for. You can get started here: https://logal.dev/projects/owncastsentry/
Alternatively, if you just want to discover more Owncast instances, I recommend checking out Ozoned's RUN channel here: https://matrix.to/#/#the-ozoned-run:matrix.org