I guess you are talking about syncthing-android (https://github.com/syncthing/syncthing-android) and @Catfriend1’s fork of that (https://github.com/Catfriend1/syncthing-android). Both are android wrappers running syncthing itself (no difference between the two there). Syncthing-android is essentially in maintenance mode - it still works, but not many changes happening. The fork is faster paced with added features etc.