The Rhino javascript implementation has continuations. Chris Double once stuck it in Jetty, and I threw together a horrifying proof-of-concept Seaside-like continuation-based web programming library based on that: http://homepages.kcbbs.gen.nz/tonyg/lshift_archive/a-rhino-a...

As a proof-of-concept, it was fun, but that's as far as it went :-)