Collaborative Map-Reduce in the Browser - igvita.com
http://www.igvita.com/2009/03/03/collaborative-map-reduce-in-the-browser/

After several iterations, false starts, and great conversations with Michael Nielsen, a flash of the obvious came: HTTP + Javascript! What if you could contribute to a computational (Map-Reduce) job by simply pointing your browser to a URL? Surely your social network wouldn't mind opening a background tab to help you crunch a dataset or two!