StudioBookings has an easy way of letting studios have a virtual waiting list for all classes.
This work well for those classes that fill up often and quickly. The system will let members go on a waiting list and if a spot opens up, due to cancellation, etc the first person in line gets added to the class automatically. If a second person cancels, the next person in line on the waiting list gets added.
The system will send the member an email letting them know they are off the waiting list for the class. If they are not added to the class, those still on the waiting list when the class starts will have their credit that was used to go on the waiting list refunded.
To set your waiting list number, go to 'Settings' and 'Business Settings'
The number you put will be the amount of people you will allow to be waiting.