Tesseract does :)
https://tesseract.dubvee.org/communities
I wrote that in a long time ago, and it's made discoverability much better. It won't show this if you're not logged in, but it does indicate if you're already subscribed to a community, and you can also one-click subscribe to the remote communities your browsing. All without the copy, paste, search, "federating...", wait, click again, refresh song and dance.
Each post/comment also has a button to browse the communities of the home instance associated with it.