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.
Twilio - Brings voice and messaging to your web and mobile applications.
Doodle - Make meetings happen. With Doodle, scheduling becomes quick and easy.
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.
Calendly - Say goodbye to phone and email tag for finding the perfect meeting time with Calendly. It's 100% free, super easy to use and you'll love our customer service.
Nexmo - Nexmo is a simple two way SMS API with global reach and wholesale rates