https://github.com/dessant/buster

I think they just have multiple test instances to test federation between them.

None of the options are that great right now. I still mostly use Jerboa, and go to the PWA for things that don’t work. Other android apps you can check out are thunder that has an alpha out, memmy which only has an iOS beta so far, but plans to be cross-platform, and lemmur which is outdated and is incompatible with current lemmy, although there’s a fork with more recent development so it could possibly come back at some point.