This project is (starting to be) maintained again.
The master branch is rather outdated (and will stay that way for the time being).
The work of bringing this project up-to-date with current libs can be found at the update-to-2016-deps branch.
diagrams-opengl is a very immature backend for diagrams. Diagrams is a powerful, flexible, declarative domain-specific language for creating vector graphics, using the Haskell programming language.
Eventually OpenGL should render both 2D and 3D Diagrams. The 2D works now, but there's a fair bit of work making it less buggy. Right now, for 3D, your best bet is the POV-Ray Backend.
If you want to contribute, there's work to be done both on the OpenGL side (writing shaders, translating the 2D Haskell code to 3D) and on the library design side (adding 3D primitives and useful functions for working with them).