It's implemented as a Java servlet using Kawa Scheme for run-time page compilation. (It's a template engine like PHP or JSP.) Pages are recompiled when modified; it's very easy to develop with.
Read all about it at brl.sourceforge.net
[Isn't CLiki supposed to list only Common Lisp resources?]
Yes, but I think it said "Lisp" when I first put this in here. I'm removing the link from "web resources" but won't erase everything on the page in case someone links to this.