pdoMap is a robust PHP ORM with many OOP features. The mapping structure, requests, and transactions are defined in XML files. The core directly generates PHP classes for high performance. It is very easy to use and configure. It features fully optimized code, caching data, a full lazy loading system, and an open system for extending all functionality.
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.
NORM is a simple ORM for PHP. It works with PDO and MySQL. Unlike other ORMs, NORM is neither complicated, convoluted, nor daunting. You can easily throw a regular object at NORM, tie in a couple other objects to relate to it, store it in a database, and return it as a regular associative array or regular object that you can toss into JSON output or a template. It lets you create and store your objects without worrying about SQL, since NORM takes care of building and managing database tables.