- OpenRemote
- SmartThings - Developers and Store
- MakerSwarm
- RaZberry - Z-wave for Raspberry Pi
- Nimbits
- ioBridge - complete stack
- NinjaBlocks - sensors, devices, and programmable hub
- Limitless LED - programmable lights
- WEMO - Belkin home automation devices
- Alyt - Android-based home security and automation hub & devices
- TinkerForge - Stackable, programmable boards. Appears to be simpler than Arduino in many ways.
- Arduino - Everyone's favorite open-source microcontroller
- BeagleBone Black
- Raspberry Pi
- Galago -
- Intel Galileo - open-source board from Intel
I will try to expand this list over time. If you have more, please add them in the comments. Thanks!