  The growing popularity of online services and IoT platforms along with
increased developer's access to devices and services through RESTful APIs is
giving rise to a new class of frameworks that support trigger-action
programming. These frameworks provide an interface for end-users to bridge
different RESTful APIs in a trigger-action model and easily create automated
tasks across diverse platforms. Past work has characterized the space of
user-created trigger-action combinations in the context of IFTTT, a popular
trigger-action framework. In this work, we characterize the space of possible
functionality that such frameworks open up to end-users in the context of two
major frameworks -IFTTT and Zapier- and discuss results from our comparative
analysis of these frameworks. We create a snapshot of 6406 triggers and actions
from 1051 channels/apps across these two frameworks and compare the available
functions, distribution of channels, and functions shared between them. We
examine user's ability to define their own channels, triggers, and actions;
analyze the growth of these frameworks; and discuss future research
opportunities in this domain.
