Is there a booking system plugin of any sort? I want to create a calendar event and attach a booking system to it. I know I can do it with a custom form, but the user cannot go back and edit their booking.
There is currently no event management or user registration functionality in Matrix's calendar system.
No, but Matrix doesn't provide comprehensive functionality for any "system" out of the box.
You could build an event management system in Matrix if you wanted :)
Matrix can't do event registrations in any way, i.e. flagging a particular event with a number of available seats and having an interface to register/unregister yourself (or others) from an event.