Hinclude.js

“Tired of regenerating HTML pages from templates? Want more from Web caches? HInclude makes one thing very easy; including other bits of HTML into your Web page, using the browser.”

“Hinclude adds one element to HTML; hx:include. When the browser encounters this element, it will include the document at the end of the src attribute.”

http://mnot.github.com/hinclude/