What are some of the leading companies developing smart home technologies?
Microsoft HomeOS [1] should be mentioned here. There is a “List of home automation software” [2] maintained on Wikipedia. I can also refer you to my own Meta Guide webpages, “Dialog Systems in Smart Home Automation & Domotics (Domestic Robotics)” [3] as well as “Best Internet of Things Resources” [4].
[1] http://en.wikipedia.org/wiki/HomeOS
[1] http://en.wikipedia.org/wiki/List_of_home_automation_software
[3] http://www.meta-guide.com/home-automation
[4] http://www.meta-guide.com/home/about/best-internet-of-things-resources