RQ (Redis Queue) is a simple Python library for queueing jobs and processing them in the background with workers. It is backed by Redis and it is designed to have a low barrier to entry. It can be integrated in your web stack easily.
Github: https://github.com/rq/rq
Plans for constructing an Arduino shield which lets you stack another Atmega 126 or 328 in master/slave configuration. Double the I/O pins, double the interrupts.