Plugin Idea- RSVP/event registration

I thought this would be a good compliment to some of the calendar plugins out there and see if there are any takers. Or at the very least, get other people thinking about this;

How bout a plugin that allows people to RSVP to an event that you are hosting. It can be similar to Evite.com or Meetup.com whereby you have the following fields;

-RSVP as yes, no, or maybe. It should also show total amount for each response.
-allow for comments.

Or perhaps there is a way to use the comments field where by the post is the event details and then people can rsvp via commenting but the comments has to show the total amount of yes, no, and maybe.