Was just having a look into what kind of support there was for OpenID in the software that I use, and basically it looks like there is fairly good support. Mailman might be a bit of a trick.

MediaWiki

• Extension:OpenID

WordPress

• OpenID

Mailman

• [Code] OpenID enabled Mailman
• Re: [Mailman-Users] openID enabled mailman
• OpenID Provider for the Mailman data with Use Case