The RSVP Pro addon for JEvents Club Gold members allows the event creator to configure an event so that site visitors/registered users can record their intention to attend.
You can set a limit on the numbers attending and setup a waiting list if required.
You can take payment for attendance using Paypal, Authorize.net, Offline manual payment or Virtuemart.
You can setup complex forms to request specific information about your attendees with support for conditional fields, charges/fees dependent on the choices made by the attendee and different charges for different Joomla user groups.
A demo video of the frontend functionality is available as well as one showing some of the backend management capability - click the "More about this product" link below.
You can control which notiifcations messages are sent out and customise these on an event by event basis if required
Attendance can be subject to approval by the event creator
You can choose whether or not you allow attendance by users who are not logged in and can force confirmation of email addresses if required
You can hide events that are full from non-attendees
You can allow 'not attending' and 'maybe attending' as options - this is useful when coupled with event invitations/organising meetings
You can show a list of attendees to other attendees or to the public and can configure (to an extent) which custom fields are visible in these lists.
You can show how many attendees are signed up in your list views/latest events view and can even show a list of attendees in your monthly calendar tooltips if you want
Attendance can be restricted to invitees only if required
You can create templates of custom fields for your registration session which allow you to re-use the same forms on different events