Take a look at this:
Maybe you already have seen this. Not impressive, right? Then take a closer look. Right. This is rendered in pure software. No 3D hardware needed. I just released Irrlicht 0.14.0
, and it includes a full software rasterizer, contributed by Thomas Alten. Very kool. So, if you are looking for a stable, usable, free, open source 3D software renderer, Irrlicht is now an option.