OpenID is a distributed system of permitting authorisation between different sites, developed by LiveJournal. More information is available at http://openid.net .
What it basically means is that you can write a comment on an OpenID server (such as LiveJournal) and it will register under your Journal name.
All you have to do is login on the other site with your Journal URL (e.g. http: >//journals.jev >on.org/users/yourname/) and your comments on the other site will be signed with your name.
(You can omit the http:// and the trailing slash. Or, you can reuse this OpenID server on another site by adding an "OpenID Delegate".)