Beowulf and Open Mosix are both distributed (active/active) clustering enviorments. Open Mosix is all GPL software, with a commitment to Free Software, not just Open Source. (Read some of Richard Stallman's writings on the difference.)
Analogous, somewhat, to Red Hat and Debian.

What is interesting about the suggestion is the idea of temporary clusters -

useful for classrooms where you have to restore computers back to their original condition. The students store the setup info on floppies or usb thumbdrives.

Or building a cluster to run on a problem over the weekend, and on Monday, a simple reboot and the workstations are back to normal.