It was written as a proof-of-concept module at the last Fotango hack-day - Ash and I used my ancient mod_tt as a starting point and had a module capable of printing to the client in about 4 hours of work. Not bad. See the mod_js project page for the source code, examples and build instructions, if you want to have a look yourself.
Given all of this, mod_js is still a nice proof-of-concept, though, and could be turned into a real server-side programming language. I also quite enjoy working in C every so often. It reminds me why I don't do itmore.
Update: Ash gave it a real web page. Crazy.