Open Compute has been making noise in the data center and IT world open sourcing server and and data center design.
Something that has taken off much bigger is Arduino.
Photo by the Arduino Team
Arduino is an open-source electronics prototyping platform based on flexible, easy-to-use hardware and software. It's intended for artists, designers, hobbyists, and anyone interested in creating interactive objects or environments.
Arduino can sense the environment by receiving input from a variety of sensors and can affect its surroundings by controlling lights, motors, and other actuators. The microcontroller on the board is programmed using the Arduino programming language (based on Wiring) and the Arduino development environment (based on Processing). Arduino projects can be stand-alone or they can communicate with software running on a computer (e.g. Flash, Processing, MaxMSP).
Here is TED video of one of founders explaining how surprising Arduino's growth has been and what it has been used for.