The Stone SouperComputer: Who says your cluster has to be expensive? When it was running, this cluster at the Oak Ridge National Laboratory had 133 nodes in it, most 486s with 32MB RAM and 10 MB/s Ethernet cards.
While our first Beowulf-style parallel computer isn’t built out of the most impressive hardware, we got tired of fighting for funding and went ahead with what we could find. Much like the classic Tale of Stone Soup, many individuals contributed to the existing machine*. Because of a complete lack of funding, we used surplus personal computers donated by individuals from ORNL, the Procurement Dept., Y-12, and K-25, to build a parallel computer system which uses public domain compilers and message passing libraries. This system was built at literally no cost.
This was back in the late 90s, so 66MHz wasn’t that slow. Still, pretty darn slow.