cl-prevalance can be found here
http://common-lisp.net/project/cl-prevalence/
and is pretty much feature-complete with regards to the original Prevalence white-paper.
I've used it in the past as the back-end for custom made content management systems instead of a relational database.
There's no real active development because there's just not much work to do on except maybe bug fixes.
I'm pretty sure Sven (the author) accepts patches if you would want to improve something or fix bugs.