The thing with ATProto is, there is little incentive in creating apps that speak the app.bsky vocabulary. If I understand correctly, there is one other full-fledged app that does that, Blacksky [0]. By full-fledged, I mean they host a PDS, a relay, an app view, a moderation service, and a bunch of feeds and other doodads. If Bluesky goes down, Blacksky will probably be fine. They are, however, yet another US company [1], which is not ideal.
[0]: https://docs.blacksky.community/
[1]: https://blackskyweb.xyz/about/support/tos/#:~:text=Blacksky%...