What type of 3D game would you like to see on OS9?
An ultra-barebones Action RPG, with multiplayer support, maybe with hotseat available, but TCP/IP networking would be best.
Might be a tall order, though. Can be 3D, or "2.5D", but even plain 2D pixel art would be fine, could even be black & white...
Something like this?
(Screenshot of Seiken Densetsu, the first "Mana series" game, for Game Boy, prequel to Secret of Mana and Seiken Densetsu 3)
Maybe it could look even more simple and blocky than this, I would not mind. Mechanics & core engine first!
Then you could even release that as your Nintendo DS homebrew project, as well... AND as a native Mac OS project simultaneously, all done using the same C/C++? *wink wink*