With Breakout, accessing all of the digital and analog pins on the Arduino is quite straightforward. One can create a web interface for both input and output. A number of examples are provided, such as using buttons to turn a LED on and off, displaying the state of a physical pushbutton and graphing the value of an analog input.
If you’re curious, and have an Arduino nearby, try out the getting started examples, you’ll have a web controlled circuit running in just a few minutes.
Diagram from breakout.js
via Smart Interaction Lab