CallME's RESTful click-to-call API allows you to integrate Click-to-Call into your website as connect any phone number to another number easily. The service provides calling from a browser, voice messaging and a few other telephony features.
Rebel is known for its interactive emails. But, developers had asked for Rebel to launch an API that allowed them to build emails with JSON (same process as Rebel Actionable API) without the need for interactive functionality. In response, Rebel has launched the Rebel Lite API.