Blender 2.64 is currently available for download for Windows, Mac and Linux, although the release is just a test build, so modifications will ensue.
This rough version of the application contains numerous improvements and fixes touching on, but not limited to BMesh modeling system, the game engine, sculpting, motion tracking and Cycles rendering engine, which sports a new non-progressive integrator and multi-threaded BVH building.
New nodes have been added (Light Falloff, Object Info, Particle Info) and sculpting receives a skin modifier for generating a mesh skin from an edge skeleton.
Furthermore, greens-screen keying has become an easier procedure thanks to two new modes; one produces gradiented plate to deal with uneven color of green screen and the other permits creating mattes faster.
The modifications for Motion Tracker include implementation of planar tracking and some small improvements like dopesheet view and tripod solving.
You can read the complete list of changes for this release on this page
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