Zen Planner - Zen Planner's fitness membership management software helps you grow your box, gym or studio with scheduling, automated billing & more. Try it now for free!
MakePlans - Online appointment booking - MakePlans
Glofox - Powerful Gym and Studio Management Software.
Appointment Booking Calendar - With the Appointment Booking Calendar you can accept online bookings from a set of available time-slots in the calendar.
Pike13 - Pike13 provides a mobile-first solution for "on-the-go" owners of small service business who are trapped in a paper world trying to manage their clients.
Dudle - Dudle is an online scheduling application, which is free and open source.