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!
A project I am most excited about is https://github.com/derivator/tafkars/tree/main/tafkars-lemmy It’s a translation layer between the reddit API and Lemmy API. If this succeeds, the existing reddit apps can start supporting Lemmy.