XDB2 is a "document" in memory persistant db written in CL.
It has build in support for versioning because it was written for time sensitive data, but you don't have to use versioning.
It is stable, and has been used in commercial environments for the last year or so.
The test files give an indication of how to use it but they are a bit dated.
If you would like more info or need help using it leave a message.