XNS (eXtensible Name Service) is:

"a new open protocol and open-source platform for universal addressing, automated data exchange, and privacy control. XNS is based on two key technologies: XML, the new global standard for platform-independent information exchange, and web agents, a patented new technology that automates the exchange, linking, and synchronization of information between publishers and subscribers over digital networks."

08/14/04 update: This has been renamed XDI in June 2004:

"a non-profit organization entrusted with the development, application, and governance of infrastructure that enables individuals and organizations to control their identity and form private, secure, trusted network relationships. This infrastructure is based on new technology donated to XDI.ORG to become a royalty-free open standard, enabling the Internet to reach its full potential."