Supercomputers and clusters are pretty different. For commercial applications, it's much more common to form clusters out of many commodity parts. Any large and

Supercomputers and clusters are pretty different. For commercial applications, it's much more common to form clusters out of many commodity parts. Any large and complicated web site probably has clusters backing it up. Things like web search, mapping websites, anything hosting a large amount of data like Youtube or Flickr. In fact basically anything that comes from Yahoo, Amazon, Google, etc probably runs on a cluster. Open source cluster software seems a lot less common than other open source stuff... the problem is, it takes a lot of work to keep a cluster running, and that work ends up being very specific to the details of cluster setup. It's too bad there aren't clusters available in general for people to play with, although with things like the Amazon services you can get close.