"Versant have come up with an easy to use object-database.Next to using relational databases, development is pain-free"
http://we-fearless-ones.blogspot.com/2009/06/db4o-object-database.html
"db4o is an object database which means there is no mapping files, attributes or other ‘impedance mismatch’ between your c# classes and the ‘database’ itself. It’s mostly used in embedded scenarios but appears to be getting used in websites. I’ve only just scratched the surface with it here, but i think it’s very cool and i hope it gains more and more traction."
Keith Patton