Mozilla WebThings is pretty cool. The gateway software runs on a Pi. They have their own open protocol over wifi or you can use ie. a ZigBee adapter. I've played with it and I think it has a lot of potential.
ZigBee & Z-Wave work out of the box, very broad device support, writing templates for new devices is pretty straightforward.
https://www.gearbrain.com/iris-lowes-arcus-smart-home-263347...
Best Buy just shut down their IoT offering, open sourced nothing and gave no refunds.