DRI, which stands for Direct Rendering Infrastructure, is a framework for allowing direct access to graphics hardware in a safe and efficient manner to provide OpenGL implementations.
I worked together with Leif Delgass on the Mach64 driver, initially written by Gareth Hughes. The driver is nearly complete, and more details about its status can be found in the DRI Wiki entry about Mach64.
I was the author of the DRI Developer's FAQ — a guide for those interested in participating on the DRI development which covers frequently asked questions about the DRI architecture, implementation details, hardware specifics and debugging. All the content of the FAQ has been merged into the DRI Wiki.