• Link - SemWeb Tools for PHP

Update 3/26/2008 - ARC completely reimplemented and released as ARC2.

Update 7/25/2008 - added Triplify 0.3 section.

From the ARC site:

ARC is a lightweight, SPARQL-enabled RDF system for mainstream Web projects. It is written in PHP and has been optimized for shared (or otherwise performance- or privilege-limited) Web environments.

ARC facilitates the integration of RDF and SPARQL functionality in PHP/MySQL-driven frameworks.

Triplify.org has released a mid-beta version of the RDF-triple to relational database mapping tools that [provides a good set of features in a small package ( about 26K ).