This is the code accompanying the two ROS rosserial AVR tutorials:
Using rosserial with AVR and UART: http://www.ros.org/wiki/rosserial_client/Tutorials/Using%20rosserial%20with%20AVR%20and%20UART
Using rosserial with AVR and USB: http://www.ros.org/wiki/rosserial_client/Tutorials/Using%20rosserial%20with%20AVR%20and%20USB
The master branch only contains the files common to both tutorials. Checkout the "uart" branch to get the full source for UART tutorial, and checkout the "lufa" branch to get the full source for USB tutorial.