The Zend Framework is an open source object-oriented web application framework for PHP used by parties large and small for building mission-critical web applications. As of release 1.5, the Zend Framework now includes support for accepting Information Cards. Read about it in Chapter 18 of the Zend Framework Programmer’s Reference Guide: Zend_InfoCard.
Furthermore, the Zend Information Card implementation can be used either as part of the Zend Framework or independently. A standalone download is available here.