[throwawayish]

http://zodb.org/ is literally what you are describing :)

It's the basis of most Zope apps, including Plone, but also many other applications; there's not much talk about it, because it just works. Like in the comment I made below; if it's a good fit ze ZODB is quite literally worth every LoC in gold.

The database itself doesn't do that much (apart from giving you transparent object/application persistence, transactions and MVCC :), as one would expect.

The Zope people made an excellent job of modularising it (or, in other words: this is by principle extremely modular), so there are a bunch of packages commonly used around it (eg. BTrees, zodburi, often either ZEO or RelStorage and stuff like eg. zope.container).

(Historically it's also very interesting - development started in 1997! The revision history is an interesting read, too, many familiar names pop up, including GvR)