Twilio - Brings voice and messaging to your web and mobile applications.
Checkfront - Checkfront is built for Tour & Activity Operators, Rental companies and Accommodation providers. Manage your inventories online, centralize reservations, process payments and get unified access to leading distribution channels.
Nexmo - Nexmo is a simple two way SMS API with global reach and wholesale rates
SnapCalendar.io - Automate scheduling with our app: no more manual reminders. Reduce no-shows, boost visits.
Clockwork SMS - Clockwork is an Easy Text Message API. An SMS API for Developers. Build powerful apps and include SMS. Signup is free, Try it now.
SimplyBook.me - Online scheduling software that offers you a beautiful customisable booking website (or widget to your own website) to accept bookings and payments with the possibility of selling products as well.