Nuclide

Nuclide is a Software Development Kit, built around the workflow in id Tech derived engines, with focus on advanced features and clean-room implementations of true-and-tested game-logic frameworks.

All of this is written in QuakeC, but there's also some GLSL part of it as well. However they can be extended and modified to suit whatever game you might need.

It pulls concepts from GoldSrc, id Tech 4 and the Source Engine 2004. It is however not a fork, nor does it use any code from these projects. This is a pure clean-room effort to make something that works for us folks here.