OpenID is a decentralized digital identity system, in which a user's online identity is linked to a URl, and can be verified by remote servers.
An open and decentralized identity system, designed "not to crumble if one company turns evil or goes out of business". Official site, with description, specifications, documentation, and resources.
Provides resources for users and developers.
Sam Ruby: OpenID for non-SuperUsers
Weblog article explaining how the technically minded can set up their own OpenID identity.
Encyclopedia article, with description, technical details, adoption progress, and criticisms.
ZDNet: The case for OpenID
News article by Phil Becker and Eric Norlin outlining the advantages of the system.