I've just released the first beta of Pydirs, a very simple object database that uses a directory structure for storage. It can be found here:
Or directly downloaded from:
Pydirs has the following features:
* easy to understand (the library is less than 500 lines) * the storage format is easy to read and even modify, using plain OS tools * transaction support * hooks for logging, debugging, caching, etc. * starts fast, so suitable for CGI and WSGI environments * lazy data retrieval
Note that Pydirs uses the Py lib for file system access and unit tests.
I hope you find it useful, if you have questions, remarks, etc. let me know!