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.
Nitro is a really easy to use, very customizable, and extensible ORM for CodeIgniter. It's pure PHP, which means you won't have to install any commandline tools to run it, just one mapping file (or as many as you like), which is as simple as defining a PHP array, and let Nitro create the classes and manage the relations.
The YB.ORM library aims to simplify writing C++ code that has to deal with SQL databases. The goal is to provide a convenient interface like SQLAlchemy (Python) or Hibernate (Java). The library itself is cross-platform and supports a variety of SQL dialects: SQLite3, MySQL, Postgres, Oracle, and Firebird. Integration with Boost, Qt4, and wxWidgets is built-in. In a typical usage scenario, you would describe your database schema and table relationships in a simple XML-based format, generate SQL code to populate database schema with tables, generate C++ classes, add application-specific logic to the classes, and use these classes in cooperation with the Session object to query objects from the database, create new or modify/delete existing objects, or link and unlink objects using relations. Simple serialization to XML is supported along with connection pooling.