LEGO Mindstorms NXT is a programmable robotics kit released by LEGO in late July 2006. It replaced the first-generation Lego Mindstorms rcx (Robotics Invention System), and was replaced by the third-generation ev3 in Fall 2013.
The base kit ships in two versions: the Retail Version (sets #8527 and #8547) and the Education Base Set (set #9797). It comes with the NXT-G programming software, but a variety of unofficial languages exist, such as NXC, NBC, leJOS NXJ, and RobotC. A new version of the set, the Lego Mindstorms NXT 2.0, was released on August 1, 2009, featuring a color sensor and other upgraded capabilities.
See the following question for details of the differences between NXT and its precursor RCX.