This is a small device designed to receive and transmit PS2 commands. The ATmega168 can receive PS2 commands from a mouse or keyboard and pass them out to a terminal or computer. Power is obtained from the computer or terminal over PS2. This device was originally designed to count the number of keystrokes in our Key Counter tutorial. A good, simple development board for the ATmega168 and the PS2 protocol.
PS2 keyboard key counter: [Link]