Ceres Solver - A Nonlinear Least Squares Solver
This is a key component of Street View. We're really happy to have released this. When we started writing Ceres, there was nothing available like it. It's state of the art; a real contribution to computer vision and other fields which need large scale nonlinear least squares.
Part of the reason I worked on this in my spare time (my real job at Google is something else) was to get it integrated in libmv (http://code.google.com/p/libmv) and subsequently integrated into Blender. This opens the door to many sophisticated tracking features, like autocalibration, rolling shutter, multi-shot solves, tripod solves, planar tracking, and more.
Blender got integrated matchmoving / tracking with the 2.61 release, by way of libmv (which I am the BDFL of). A critical part of many tasks in 3D reconstruction and tracking is a solid, flexible nonlinear minimizer. Since Ceres is so easy to model problems with, is so fast, and is appropriately licensed (unlike some alternatives), it is an enabler for these more sophisticated tracking operations.
Note that Blender's next open movie, http://mango.blender.org, is live-action done with Blender's tracking tools. Ceres is going to be used for that as well.