Darkmatter is a project mainly written in OBJECTIVE-C and C, it's free.
OpenGL-based game engine in ObjC
An OpenGL-based game engine written in Objective-C.
The Darkmatter/ directory contains the source for the Darkmatter engine. The Xcode project compiles the engine as a framework, which is linked to by the demo app in the DarkmatterDemo/ directory.
The latest version of the source can be found at https://github.com/mattrubin/Darkmatter.