HyperInvite

Hyprinvite is a web application which complements the way we invite friends and manage the attendance, we do not require all the email of all your guests. Sending a party no. + the password to your friends is much more elegant than a long messy email or sms. Best of all, you get to interact and pass messages to them before they attend.
Hyprinvite takes advantage of the ease and privacy of using open ID technology to create a group for an event.
More at:www.hyperinvite.com