Yadis is a service discovery system allowing relying parties
(aka identity consumers or membersites) to determine automatically,
without end-user intervention, the most appropriate protocol to use.

Examples of such services are:

* Single sign-on across web sites
* Profile exchange and form filling
* Blog anti-spam

Yadis provides the first step for any service that uses identifiers for
authentication, accountability, privacy controlled data exchange and more.