Jacques Fuentes has submitted some information about an ActiveRecord tool he's developed that's similar to the pattern found in Ruby On Rails and can be found here.

It is extremely similar to ActiveRecord for Ruby on Rails. We believe our project is offering a better programming experience than propel/doctrine since it does not require effort to get started. Propel/doctrine both require that you use yaml/xml files or column mapping in your model classes. We use show fields to 'magically' load this in the background eliminating the tedious requirement of mapping your schema to a file.

The code makes use of some of the features of the upcoming PHP 5.3 release (but won't work with versions prior to that). If you'd like to try it out, you can grab the code here.