Good PHP ORM Library?

Is there a good object-relational-mapping library for PHP?

I know of PDO/ADO, but they seem to only provide abstraction of differences between database vendors not an actual mapping between the domain model and the relational model. I’m looking for a PHP library that functions similarly to the way Hibernate does for Java and NHibernate does for .NET.

Look into Doctrine.

Doctrine 1.2 implements Active Record. Doctrine 2+ is a DataMapper ORM.

Also, check out Xyster. It’s based on the Data Mapper pattern.

Also, take a look at DataMapper vs. Active Record.