Prompted by Google's recent acquisition of Nest, the folks at Spark.io were inspired to create an open source alternative -- note the use of alternative, not equivalent -- which they succeeded in doing over the course of a single day. The project was detailed on the Spark Blog today, complete with short videos and downloads via Github.
The project is built upon the Spark Core, which is Spark.io's $39 offering, and Spark's WiFI development kit/Spark Cloud. From there, a stated 3.5 engineers worked from 10AM until 3AM to finish the project -- the half engineer is represent by one who decided to go to bed early, apparently. The total cost, including the materials to build its shell and the Spark Core, worked out to about $70 USD.
The thermostat itself was made using wood and acrylic, which the makers say were better choices for whipping together a (rather nice looking) prototype. Beyond those and the Spark Core, a Honeywell HumidIcon sensor was used for temperature and humidity, LEDs were used as indicators and for the display, and a Panasonic PIR motion detector was used to tell if a person is home or not.