redbean

RedBeanPHP is a zero-config, easy-to-use object database for PHP and an ORM tool. It works very simply. Just create bean objects and throw them at RedBean. RedBean will analyze your objects and infer a readable, comfortable data scheme from it and create all required tables and columns on the fly. RedBean is not schemaless, it makes neat tables and columns for you, but on the fly without any configuration.
RedBean try to change the way you use ORM by eliminating the complexity of the configuration part. RedBean store objects only, and can manage object relations as well. The core of RedBean is very minimalistic for an ORM, but functionnality could be easily extended with plugins, already included : Transparent Locking, Caching and Automatic Database Optimization and Cleaning.
RedBeanPHP is open source released under BSD license. Also available for download with RedBean : RedShoe a compact PHP script that automatically syncs MySQL databases for RedBean; RedUNIT a set of Unit tests to confirm that RedBean works according to specifications; and Pre-packaged since it works well with other frameworks such Zend framework, Shozu… etc. Version 1.1 already available for download in the nightly build page and include support for SQLite 3.
More information and download at http://www.redbeanphp.com