Thunder is an open Lemmy app for iOS and Android that is currently under development. You won’t find it in any app store, so it’s not as well known as Jerboa. Still, it’s an excellent app.
The client is written in Flutter/Dart. If you have any development skills, lend a hand!
Works pretty well. Nice and stable. Naturally, it doesn’t have anything in terms of profile editing as it’s a new app, but it’s a nice start.