A C++ header library for fast operations on vectors/matrices (3D/3x3) using Streaming SIMD Extensions (SSE, SSE2, SSE3, SSE4); Tends to be used in 3D graphics applications and game developement.
Ray3d is a multi-platform 3dgame engine with an entire FPS game for it's techdemo. It's based on Irrlicht and other open source libraries, and written in C/C++. It is in pre-alpha and under HEAVY development.