Pydirs is a very simple object database written in pure Python. It allows storing Python objects in a directory structure, with subclasses of a special persistent base class stored as directories, and anything else as text files. This makes it easy to understand and debug, and makes that you can use standard OS tools to view and even modify the database.
Pydirs starts fast (so it's usable in WSGI and CGI projects), is lazy (data is only read from disk if accessed), quite scalable (though large databases will use a lot of disk space, depending on the block size of the disk), supports transactions and has hooks for logging, caching, etc. It has a simple, Pythonic API and an small, understandable code base.
Pydirs uses the py lib version 1.1.2 (tested with versions starting with 0.9.2) for file-system access and testing, which is available as a package for most UNIX-type operating systems, as an egg on PyPI, or can be built stand-alone (see the Py lib installation page for more details).
Pydirs is released under the GNU GPL license.