These are screenshots of a Quake2 level viewer I've written the past weekends.
It uses Quake2 PVS to render worlds, and it is almost identical to quake2 renderer
except for entities, warping water and dynamic lighting, which I plan to implement
sometime. I think I get pretty decent framerates out of it, 25-30 fps on a
PII-300 with ATI Rage Pro using multitexturing. There are still optimizations to be
done, like texture-sorting. It uses Direct3D for rendering.