Moonbilight is an AVR ambilight project designed for ATmega16/32 microcontroller.
It uses V-USB (http://www.obdev.at/vusb/) library to communicate with PC directly through USB port.
The GUI based on Qt (http://qt-project.org/) is designed to work on Linux and Windows (Not tested on Mac).
The project is already fully functional. However it is still beta and may contain some bugs.