OpenSAM...

One of the most comprehensive and detailed plan for bringing standard approaches and techniques to mashups is OpenSAM, which leverages many existing standards such as WebDAV, openid, LDAP, and also subscribes to DataPortability.org’s standards to create a consistent and well-organized design and interaction model for offering complex, heterogeneous mashups to both the consumer and business community.

Even more importantly, they cite a good number of companies already offering Web applications that support OpenSAM. The OpenSAM vision is broad and focused across the usage spectrum and the OpenSAM folks say that “once OpenSAM is added to an application, it can immediately join mashups with all other OpenSAM applications.”

Source: http://blogs.zdnet.com/Hinchcliffe/?p=162