db4o - Open Source Object Database
Got heard of this from Johnson, and it looks promising from the site's reviews and comments.
It supports 3 type of query methods:
2) Native Query
3) SODA Query API
It looks pretty good, until I read this on the CascadeOnDelete:
"Houston, we have a problem - and there's no simple solution at hand. Currently db4o does not check whether objects to be deleted are referenced anywhere else, so please be very careful when using this feature."
However, as long as you don't make use of this Cascading feature, you are safe from hassle of debugging your apps for some unexpected behavior.
Running out of time and I've used this to built my prototype web apps and it indeed save me lots of time writing SQLs, guess I'll be using it until my data structure and my DAL is out.