Have the ability tp define resources and their availability for booking.
For example, at a Hair Salon you could have multiple Hair Stylists - Sally, Sue and Becky.
Sally is available only on Mon/Tues/Wed
Sue is available Mon/Wed/Fri
Becky is available Thurs/Fri/Sat
Each individual stylists is defined as a "resource" and can also have Holidays/vacations (periods of non-availability) defined too.
Resources can then be optionally selected by the customer at checkout OR the resource availability gets calculated across ALL available resources to provide the total availability (number and days).
This could also be used for Rooms, and any other resource who's availability affects the booking process.
http://wpbookingcalendar.com/ has this functionality built in but is not compatible with Woo Commerce.
Planned for release in version 2.4.