For several years now I have been working on my own 3D game engine, originally intended for the 3D version of Seed of Chaos, but although that project never got off the ground I still work on the engine for educational purposes and for other personal projects. The engine is written in C# and uses XNA, mainly for the graphics device and math library. The Scene, Model, Mesh, Material classes etc are all custom taylored for the engine. I have also recently integrated the Bullet Physics Engine.

Below is a brief list of Engine features:

-Real-time per-pixel lighting with normal mapping with several light types

-Normal mapped ambient pass with placeable ambient lights to vary color and intensity of ambient lighting in the environment, blended with ambient occlusion.

-Supports light maps for ambient and global illumination

-Real-time soft shadows and projected texture effects on light sources  

-Utilizes the Bullet Physics Engine for rigid body physics and ragdoll

-Collision detection and character animation

-Flexible scene system allowing various game types to be made easily with the engine (i.e. the engine is just as suited for making an RTS as it would be for a FPS).