SimpleScene is an scene manager for C# and OpenTK, released into the public domain. It's primarily intended for educational purposes, and as a starter-kit for those who want to get their hands dirty learning OpenGL and GLSL.
There is a GLSL120 shader which supports per-pixel light from a single GL-light, as well as single-pass wireframes. It has code to render using legacy GL calls, or vertex-buffers (which are much faster), and it's own wavefrontOBJ loader. There's also an attempt at bump mapping, but it's not fully working. It currently doesn't have any space partitioning (such as octrees or bsp), nor does it have heightmap terrain. Perhaps I'll add them in the future. The bonus of it *not* having those things and many more, is that it's dirt simple and mostly easy to read the code. I try to keep it as direct as possible with few abstractions.
The Scene manager comes with a sample program, WavefrontOBJLoader, which loads a skybox, a spaceship 3d model, and paints some stars into the skybox for fun.