OpenID is an open standard for cross-site authentication on the Web. It's a very lightweight protocol in which an individuals identity is tied to a specific URL. Whenever the individual needs to log in to a website, they can simply provide their URL as a user identifier, and an OpenID-enabled website will redirect the user to that URL for authentication. There are also standard extensions that allow the user to control what (if any) information about them their OpenID server makes available to third parties. You can read more about OpenID at openid.net.
NSMWiki supports the use of OpenID for user logins. We intend for this to be a pretty open wiki, so we will accept pretty much any OpenID server out there. If you can log in to there, you can log into NSMWiki. In fact, if you have OpenID but no NSMWiki account, the simple act of logging in to the wiki with your OpenID is enough to create your wiki account. It's actually pretty neat.
If you have an existing (password-based) wiki account, and would like to convert to using OpenID, simply log in with your password and then visit the Special:OpenIDConvert page. Be warned, though! Once you convert to OpenID, you cannot switch back to using a password!