Yes we do!
Fuze has application programming interfaces (APIs) that allow users who have already authenticated themselves using another application to automatically be authenticated in Fuze.  The interface does require some work on the non-Fuze web application, but it generally is pretty easy and no sensitive information is passed to or from Fuze that has any potential to diminish the integrity of the other application.
For instance, the Fuze single sign-on APIs allow you to provide single sign-on capabilities (SSO) with online banking applications, other Web-based applications used to authenticate consumers as well as for staff using Active Directory and LDAP to authenticate on their network.  The only requirement is that the application being used with the Fuze SSO API must be able to create a dynamic https link that includes query-string variables.

We also offer SSO with Twitter and FaceBook