Cognitor is an OpenID based Single Sign On Service (SSO) for web applications. If you have multiple applications or one portal that consists of multiple decoupled web applications that share the same user base, Cognitor can manage those users and allows the user to login once for all applications.
Because Cognitor uses OpenID it is not limited to the domain boundaries like cookies would be.
The goal is to have a small, stateless, extensible and configurable application that can be integrated into an existing environment by customizing the persistence.
For more information go to the wiki: http://github.com/patka/cognitor/wiki