I've released yet another toy project: an attempt to create a PHP ORM. It is hosted on BitBucket

The project grew out of disappointment with Doctrine and its numerous bugs (problems with isset, saving already deleted object etc). It uses mostly well-known patterns: Unit of Work, Identity Map, Mapper and more. Internal methods are unfortunately public due to some limitations of PHP (no package access nor friend classes), with alternatives (using reflection or classkit or much more sophisticated design) felt like unneccessary complication.

There is almost no documentation yet, feel free to drop a line if you are interested in the project.