We allready had two posts about this 3D engine in the past. now the first public non beta version is out. Here is what the author says:

Version 1.0 of The Yeti3D Engine for the GBA is now complete! Thanks to the work of Greg from Torlus Console Development, the engine now has a fully optimized 15bit dynamic lighting DDA texture mapper. The engine is now reported to run at a cool ~15-20 FPS on real hardware. The latest demo zip contains both the C and optimized ARM versions for you to try.

http://www.theteahouse.com.au/gba/