Depends on what you want to do, what you know, and how much effort you want to put in. For other ways, outside the usual Android tools, there are a couple options. With python, there’s a project called BeeWare that makes a lot of things easier to deal with.

Personally, though, I’ve been game deving in Godot, and have even made a few dumb little personal apps with it. There’s coding involved, but there’s also a lot you can do in the interface to design the app visually, and exporting to any platform is pretty straightforward. Even the Godot editor itself is made with the Godot editor, so it can do a lot of things outside games.

KeePassXC, mainly because it was the first fork I found at the time that would auto-reload the kdbx if it was modified elsewhere and you had it open. Great for a syncthing setup to share passwords between a small IT team locally.