grack Landscape Engine
The grack Landscape engine was a project I had started to learn about writing real-time 3D games. I managed to get to a point where you could run around the landscape and fly around (like in Tribes), but not much further. I had trouble with my subdivision algorithm - I think I tried to make it too complicated.
This project was a great way to learn about how to write a game loop and event system. I hadn't written something that didn't involve menus and dialogs for so long that I had forgotten how to structure the program. It's pretty straight-forward once you crack the mental block.
Homepage: http://grack.sourceforge.net