There’s a comprehensive list of Lemmy apps being curated here.

Right now I’m using Liftoff on Android.

I’ve seen this site suggested in posts like this:

I’m using the spoiler tag because elsewhere I’ve seen this warning about the site:

run by people from kiwifarms (a known bad actor on the fediverse).

I’m unfamiliar with “kiwifarms” but the site currently does has some offensive language at the bottom that’s associated with 4chan, so be warned.

That said, it appears to be the only site currently available to see which instances in the fediverse have blocked/defederated your instance. (The reverse of <instance domain>/instances, which only shows which instances your instance has blocked/defederated.)