This is the Makaqu engine, a modified Quake engine for PC and Sega Dreamcast.

Aside from the Dreamcast-specific features, like VMU support, it is identical to the PC version of Makaqu. The source code is the same for both the PC and Dreamcast versions.

This is a software-renderer-only engine. There are several great hardware-accelerated engines out there, and I wanted to try making a good software-based one.