Writing a small roguelike is the task that I use to learn/test new languages. Mine is a very simple one: you can just move the player and open doors and there are some monsters running around. But it uses bitmap graphics and things are moving in real-time [0], so it's an example covering some interesting aspects of a language and its libraries (and IDE).

[0] With real-time I mean that it is not turn based, unlike most roguelikes. It uses a future event list with time-stamped events that are waiting to happen.