Mesa 7.7 introduces the Gallium3D work. The new OpenGL extensions now supported include GL_ARB_draw_elements_base_vertex, GL_ARB_depth_clamp, GL_NV_depth_clamp, and GL_ARB_provoking_vertex. In Mesa 7.7, the ATI R300 driver based upon the Gallium3D architecture is considered "unstable" rather than "experimental" in previous Mesa releases.
The short Mesa 7.7 RC1 release announcement can be read on Mesa3d-dev. Mesa 7.6.1 RC2 was also released at the same time, which just incorporates more fixes for stabilizing the 7.6 series.