I've been spending the last few weeks throwing around code for my own game engine. It was doing well, but eventually I realized that it's ultimately futile--by the time I implement enough features to make a good-looking game, it'll have been a year or so.
So I stopped work on my "jam" engine and checked out OGRE. It's quite neat--open source, lots of features, and it's in pure C++ (except resource loading and particle effects of course, but that's good) so I don't have to worry about clunky binaries slowing a game down.
Anyway my friend and I have been working towards perhaps developing a good fretsonfire-type game, in C++ (so it's not slowed down by python like FoF is) and supporting multiple instruments besides the guitar. We also might go the Performous route and add in a DDR-type thing but I think Stepmania has that genre covered, so probably not.
In any case the main idea is to go beyond the crappy '3d', 20FPS, jerky look of fretsonfire and develop a (open source, of course) polished guitar/rhythm game. Since I've just begun working with OGRE I don't have anything to show for it but I do have lots of exciting designs in my head (and I had a working prototype built on my Jam engine before I scrapped that).