The one issue I have with AlternativeTo is it sometimes conflates a website and an app.

Your link, YouTube, is a good example. NewPipe is a great open-source alternative to the YouTube as an app (it's a YT client), while PeerTube is an alternative to YouTube as a website (it's a video-hosting platform). Yet they're listed together.

Yep been using alternativeto for a while and they are way ahead. I built this to highlight strictly open-source projects.

The key difference is that "AlternativeTo" has voting from users, whereas "Opensource.builders" has voting (stars) from developers... not sure which is better, probably a combination of both