The libglvnd project is a new work-in-progress version of a vendor-neutral library for arbitrating OpenGL calls between multiple drivers/vendors on a per-screen basis. Basically this allows each driver to ship its own OpenGL library but to not overwrite the main system libGL file or cause any collisions with other OpenGL drivers present on the system.
Bryan Nguyn of NVIDIA announced the new vendor-neutral OpenGL dispatching library on the Mesa-dev mailing list today.
Last September, Andy Ritger proposed updating the Linux OpenGL ABI to allow for multiple vendors to co-exist within a single process and OpenGL applications to dispatch commands to different vendors with per-context granularity. The current proposal calls for a vendor-neutral "API library" which acts as an intermediate layer between the application and OpenGL vendor implementations that manages this dispatching.
I have written a work-in-progress library based on this proposal which implements this API library for GLX. This library leverages some code from Mesa's glapi module to handle TLS and core OpenGL dispatching, as well as the BSD-licensed uthash library and the X.org Xserver's list.h.
The library in its current form is hosted on GitHub.