A hardware watchdog for a Raspberry Pi. It uses an atmega328 attached to the Raspberry Pi's serial port, with a simple command line interface.
It will reset the Raspberry Pi if either a long or short watchdog timer isn't reset within a time period. It will also toggle a pin to alternate between booting to kernel_emergency.img and the normal kernel - see http://elinux.org/RPI_safe_mode . This makes it less risky to upgrading the boot image remotely. There are a few other features such as a bodgy random number generator and hmac. The 'oneshot' watchdog lets you set a failsafe so that if you try something that doesn't work, it'l reboot after a set period of time.
A rough list of functionality is in the read handler.