Simple object persistence (i.e., serialization to a file system) is what pickle, marshal and shelve do.
However, here's the next thing of some interest OODB's.
Zope's ZODB . The original OODB for Python, the backbone of Zope.
buzhug : "a fast, pure-Python database engine, using a syntax that Python programmers should find very intuitive."
PyPerSyst "fast, reliable, and flexible object persistence with a small footprint, suitable for embedding in other Python applications."
CouchDB "A stand-alone document store, [which] most closely resembles the Lotus Notes/Domino storage engine."
ObjectivityDB/Python "a high performance and robust Object-Oriented Database Management System [ODBMS]."
Axiom "Axiom is an object database, or alternatively, an object-relational mapper." The pleasant thing is that you don't really care which.
Durus "a persistent object system for applications written in the Python programming language."
http://www.itamarst.org/software/cog/ (not CoG , the Commodity Grid) is the Checkpointed Object Graph, which provides "semi-transparent persistence for large sets of interrelated Python objects."