I just sold a business that had some nice tools. I still have the rights to it because I had it created. Here is a link to a calendar that is linked to google calendars and can be modified easily. http://body4change.com/fullcalendar/calendar/
We also had a nice system that allowed clients to login for boot camps and for 1-on-1 sessions that was integrated with payroll. The calendar above most likely fits what it sounds like you’re looking for, but we used someone who can easily modify a lot of this stuff that we could refer you to. Feel free to reply to this or message me with any questions.