PHPTMAPI 3 by Johannes Schmidt.
From the webpage:
PHPTMAPI 3 is the succession project of http://phptmapi.sourceforge.net/
PHPTMAPI is a PHP5 API for creating and manipulating topic maps, based on the http://tmapi.sourceforge.net/ project. This API enables PHP developers an easy and standardized implementation of ISO/IEC 13250 Topic Maps in their applications.
What is TMAPI?
TMAPI is a programming interface for accessing and manipulating data held in a topic map. The TMAPI specification defines a set of core interfaces which must be implemented by a compliant application as well as (eventually) a set of additional interfaces which may be implemented by a compliant application or which may be built upon the core interfaces.
Please spread the word to our PHP brethren.