The Presence daemon handles awareness of available machines in the network neighbourhood. It is designed to be lightweight and cross-platform. It is available for download at http://code.google.com/p/presence-discovery/.
Scavenger is a complete cyber foraging system. It offers developers the ability to easily modify their applications to dynamically and opportunistically to take advantage of available, nearby computers. Tasks are moved and scheduled automatically by the system, depending on the capabilities of the available machines. It can be downloaded from http://code.google.com/p/scavenger-cf/. There is also a Scavenger Tutorial.