NXT is a modular robotics kit manufactured by Lego. There are ROS interfaces for the default Lego firmware (v1.28) based on the NXT-python library by Douglas Lau.
The NXT-ROS software stack provides many useful tools to interface NXT robots with ROS. Currently NXT users can take robot models created with Lego Digital Designer, and automatically convert them into robot models compatible with ROS. The converted robot model can be visualized in rviz, and in the future we hope to add simulation capabilities in gazebo, our 3D simulator. The bridge between NXT and ROS creates a ROS topic for each motor and sensor of the NXT robot.
Once a robot is connected to ROS, you can start running applications such as the base controller, wheel odometry, keyboard/joystick teleoperation, and even assisted teleoperation using the ROS navigation stack. The NXT-ROS software stack includes a number of example robot models for users to play with and to get a feel for using NXT with ROS.
Video and more information
For more information see the annoucement here.