some fun geometry shaders: fisheye projection (hardcoded subdiv, since no tesselator available), and triangle edge based sketching.
I started the cube engine(s) with lofty goals of utter simplicity and cubic worlds, but but I failed on both those accounts. Nanocube was a project purely for the sake of trying to write a full FPS game in the fewest lines of code possible, making everything (including animated characters) out of cube. This failed too, when Lee added his dual parabolic shadowmaps.
An experiment in rendering random implicit functions into an octree for use in fast raytracing. Added the usual effects (lighting, reflection, shadows, ambient occlusion).
Implicit functions are a lot of fun to create geometry with, but a bit computationally intensive for larger volumes, so we do it on the GPU. Marching Cubes then makes it into a mesh that can be rendered traditionally (very fast).