In principle this is an event booking database. It allows users to login and book into an event or cancel existing bookings. System should also be able to send emails with event details and a url link so that users can book in with a click and a password.
Allow administrator to setup site brand, logo, description, booking cut-off date, ie need to book x number of days prior to event to get a reservation.
Allow users to login with authentication by email address and password.
Allow administrator to add users & edit their details - ability to set user permissions to add/remove/maintain events.
Allow user to edit their own details.
Ability to add an event (event date, event name, event description, event cost, add invited users/groups, last booking/last cancellation date - default to x days prior to event)
Send event details by email to all invited users - email contains a link which will 'book' the member as attending the event
Allow users to book into an event, or cancel a booking. Ability to charge a fee for late cancellation etc.