Manage events among users
It should be pretty simple by creating a content type "events", with the date fields using the Date module http://drupal.org/project/date. Then adding in the signup module for users to RSVP http://drupal.org/project/signup. You can also add in the calendar module for some displays http://drupal.org/project/calendar or the full calendar module http://drupal.org/project/fullcalendar