Uber-hacker and blogger Les Orchard saw the potential of Amazon S3 early on and realized that even though it's not intended to be a consumer-facing service, with a little JavaScript and ingenuity it can be used to host entire web applications. To that end he create S3AjaxWiki, a very slick proof-of-concept wiki that exists solely on S3, no external sever required. For more information, take a look at Orchard's blog, where he's chronicling the project's progress.