Our API directory now includes 37 campaign APIs. The newest is the Experian CheetahMail API. The most popular, in terms of mashups, is the LaunchBit API. We list 1 LaunchBit mashup. Below you'll find some more stats from the directory, including the entire list of campaign APIs.
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.