Mesa 3D has famously always not been technically OpenGL (lacking certification), but times are changing: "This is a great day for Mesa and open-source graphics drivers. Just a tad over a month ago, I submitted OpenGL ES 2.0 conformance test results to Khronos for Intel Sandy Bridge and Ivy Bridge GPUs with Mesa 8.0.4. There were no objections during the 30 day review period, so we are now officially conformant! Finally being on that list is pretty cool. Not only is this great news for my team at Intel, but it's terrific news for Mesa. Mesa has had a long history with OpenGL, the ARB, and Khronos. This is, however, the first time that Mesa has ever, in any way, been listed as a conformant implementation. This is a big boost to Mesa's credibility."