CHAOS - Midnight Code; the best kind
PelicanHPC - PelicanHPC is an iso-hybrid (CD or USB) image that let's you set up a high performance...
FlashMob ISO - FlashMob ISO (OS) was custom developed by the University of San Fransisco for their supercomputer.
Rocks - Rocksclusters website
BOINC - BOINC is an open-source software platform for computing using volunteered resources
Charity Engine - Charity Engine takes enormous, expensive computing jobs and chops them into 1000s of small pieces...