Nicolas Robert has been working on a cool 3D engine:

God isn't yet a game but "only" a tech demo; I focused on the engine development rather than the gameplay, the reason being that I wanted to see what are the limits of the GBA (though, I also have my own limits ;-). Eventually it will be a real-time strategy / management game, a kind of mix between Dungeon Keeper, StarTopia and Monopoly Tycoon.

Done already:
- Presentation, using bump mapping and voxel spacing,
- Main 3D graphic engine,
- Pathfinder (core of the AI),
- Support for texts and menus,
- Support for sound and music (PCM & ADPCM).

This tech demo allows the player to move around the map, and dynamically add and remove walls. The pathfinder is activated and finds the shortest path from the building in the center of the map to any of the 4 targets in the corners (the path is computed and displayed every time the map is modified).
http://www.gbadev.org/