Mesa 13.0 was released today as what is likely the most significant release to this 3D graphics driver/library implementation ever! Mesa 13 is huge for open-source driver uses particularly with Intel, Radeon, and GeForce hardware driver improvements. During development this release was known as Mesa 12.1
OpenGL 4.5: The Intel i965 driver for Broadwell hardware and newer now supports OpenGL 4.5 compared to GL 4.3 on the previous stable release. This is a huge win and great to finally see the Intel driver catch-up to the latest OpenGL specification albeit doesn't yet support all the 2015~2015 extensions, including the extensions needed for the "AZDO" approaches. Haswell is still at OpenGL 3.3 for Mesa 13.0. The RadeonSI (AMD GCN) and Nouveau NVC0 (Fermi and newer) drivers have also implemented all OpenGL 4.4/4.5 extensions, but they only advertise OpenGL 4.3. Not until they complete the Khronos GL 4.4 / 4.5 conformance tests will that support be advertised via the OpenGL string. The Radeon crew is working on the CTS passing but they have said it's quite some work while the Nouveau developers are still working on figuring out the CTS approach with just being a community-organized driver effort.
OpenGL ES: On the OpenGL ES front, Intel Haswell now has OpenGL ES 3.1 support while Skylake and newer have finished OpenGL ES 3.2 support.
RADV Radeon Vulkan: The RADV driver was merged to mainline Mesa as an open-source Radeon Vulkan driver that made much progress over the summer (http://www.phoronix.com/vr.php?view=23596). This is the "unofficial" Radeon Vulkan driver with AMD having not yet open-sourced their promised Vulkan driver code and even AMD developers having recently referred to this as the "Red Hat driver", so it's still up in the air what will happen in the long-term for open-source AMD Vulkan support. At least RADV is making good progress for satisfying Linux gamers now and can successfully run The Talos Principle, vkQuake, and Dota 2 Vulkan-enabled Linux games. The RADV driver works in conjunction with the AMDGPU kernel driver meaning support by default for GCN 1.2 GPUs and newer or GCN 1.0/1.1 if you manually enable the experimental AMDGPU support in the kernel.
Better Intel Vulkan Driver: Intel's "ANV" Vulkan driver is in much better shape now than when it premeiered in Mesa 12.0. There has been performance optimizations, many fixes, and other feature improvements for this open-source Vulkan driver that is supported the best on Broadwell and newer while the Haswell support may still vary.
Nouveau Pascal: Early work on Pascal support in NVC0 but it is only relevant for the GP100 and not the consumer GeForce GTX 1000 series hardware, until NVIDIA releases the signed firmware images to Nouveau developers.
Better RadeonSI Performance: The open-source RadeonSI driver has seen a number of performance improvements. Upgrading is very much worthwhile for users of the open-source AMD driver stack.
Gallium Nine: There have been many improvements to the Gallium3D Direct3D 9 state tracker. So far this state tracker is only useful if patching Wine to support using this D3D9 implementation when running your Windows games on Linux.
Mesa development was extremely fast-paced this year and is at nearly two million lines of code. As great as Mesa 13 is, there are some features you won't find in Mesa 13.0.