One of the things I've been working on recently at my new company is a PHP-based managed infocard Secure Token Service, the Carillon STS, compatible with Windows CardSpace.
There's long been a PHP Relying Party freely available for CardSpace, but there's only been a Java-based open-source managed STS until now. Our new STS, combined with the firefox identity-selector plugin, makes it that much easier for anyone to experiment with CardSpace using free, interoperable tools.
Happily, Kim Cameron (Microsoft's CardSpace architect) has waxed enthusiastic about our work, including its support for X.509-certificate-based authentication for CardSpace.
Of course there's plenty of work still to be done, but positive feedback about an initial release is always nice!