I've been looking at a lot of tools for enterprise software development recently.
DataNucleus is one of the most interesting.

It doesn't do anything new and it doesn't do anything that any number of tools can do better.

They want to be the last-word and one-stop-shop for large-scale data access.

They provide JPA, JDO and REST bindings to all different kinds of data stores: RDBMS, OODBMS, SimpleDB, Hadoop HBASE, etc.

Google uses it as the persistence engine for their AppEngine platform.  It is almost laughably simple to use with their schema-less data store.