If Devtest was too complicated for you, and you felt lost in the details, just play this instead. None of those ugly textures or block choices. I guess it's basically the same as Cave Game in many respects.
Ok, now for the serious part. I have started trying to mod without default. It actually isn't too bad. And this is an excellent tool to help. If your mod requires default, this will break it. Which could help you figure out why your mod doesn't work with some other game.