You might find this interesting http://www.kuwata-lab.com/kwartz/ from the Ruby crowd.
I think that's pretty different in motivation, if I understand what they are doing. It reminds me of XMLC and similar products, but with a more CSS-ish feel. It's also about separating Business Logic from Presentation Logic, and WSGIOverlay doesn't do that in the slightest. It's really more about separating site composition from the templating of individual applications.# Ian Bicking