The extension that Ian Romanick of Intel has been working on is for the OpenGL GL_ARB_viewport_array extension, which is a means of exposing multiple viewports. As explained in this GL 4.1 tutorial, "GL_ARB_viewport_array provides a mechanism to expose multiple viewports, each specified as a rectangle. The destination viewport may be selected per-primitive by the geometry shader. This allows the Geometry Shader to produce different versions of primitives destined for separate viewport rectangles on the same surface. Additionally, when combined with multiple framebuffer attachments, it allows a different viewport rectangle to be selected for each. This extension also exposes a separate scissor rectangle for each viewport. Finally, the viewport bounds are now floating point quantities allowing fractional pixel offsets to be applied during the viewport transform."
The GL_ARB_viewport_array extension is documented in full at OpenGL.org.
Ian sent out the initial viewport_array patches one week ago but now with the second revision he believes the Mesa code is in good shape and hopes to land the code in mainline Mesa by early next week. The set of 37 patches can be found on the Mesa-dev list and provides support for this OpenGL extension to core Mesa and is then hooked up by the i965 Mesa DRI driver. This extension for the Intel driver only works with Intel Ivy Bridge "Gen7" graphics and newer when using an OpenGL core context profile due to its dependence on OpenGL Geometry Shaders.