Proto

Proto is a self-contained webpage that can export and import data URIs, and load its own source. Here it is as a data URI, and here it is as an HTML file. Since Chrome is a bit anal about data URIs, and Firefox is even more so, to use the data URI version you'll have to copy the link text and paste it into your address bar. When bootstrapping Proto’s source, the data URI is better than the HTML file because some whitespace is lost when using the HTML version, but all other features should work fine.