Inspired by Metacarta's Map Rectifier, this is an open source map warping / geo rectifying service, written in Ruby and Rails. I've customised it with the OpenStreetMap project in mind. It's MIT licenced, so you can play with it if you want too!.
Libraries and other institutions have used it, including the New York Public Library, Harvard and Stanford Universities.
Tim Waters
tim@geothings.net
blog: http://thinkwhere.wordpress.com