A simple "who wants to go kayaking" registration

Hi

I am running a simple web-site for a kayaking club.

What I need is a simple Widget where members can sign up for a trip, event or just a night in the cinema.

Example:
– I create an event called “Who wants to go kayaking friday the 1’st ?”.
– People who are already signed up to get notifications like this, gets an e-mail with the invitation. And they can register for this particular event.
– I (as the event creator) can easily require a list of participants.

There are many complicated event manager plugins, but I can’t seem to find a simple tool for this.

Any suggestions ?

Thanks
Kris