For a November 2017 overview, see this Zapier Blog Post comparing many different options. Also, Hubspot has a good overview from their blog updated in January 2018.
- Plann3r
- TimeTrade
- x.ai
- Doodle
- Stonewall Solutions (Rhode Island Company)
- Acuity Scheduling
- GigaBook
- MyTime
- ScheduleOnce
- SetMore
- YouCanBookMe
- Booker.com
- MindBodyOnline
- Yocale
- Appointlet
- SimplyBook
- vCita - kind of a CRM, but with appointment scheduling built in.
- PlanYo
- Skedda
- SuperSaas