Twilio - Brings voice and messaging to your web and mobile applications.
Kissflow - Kissflow is a workflow tool & business process workflow management software to automate your workflow process. Rated #1 cloud workflow software in Google Apps Marketplace.
Plivo - Plivo simplifies your customer engagement.
Pipefy - Pipefy is a process management software that empowers anyone to create and automate efficient workflows on their own without code.
Nexmo - Nexmo is a simple two way SMS API with global reach and wholesale rates
Process Street - Create beautiful rich process documents in a simple to follow checklist format. Fast, free and incredibly simple to use.