In lieu of answering this question here, I have made a new Meta-Guide.com webpage on “Dialog Systems in Smart Home Automation & Domotics (Domestic Robotics)” [1]. This webpage was created by extracting all relevant references from my four years of tweets as well as from my Meta Guide website itself.
Although not open source, I imagine that the new Microsoft HomeOS [2] could be used with the Kinect for Windows [3], which has speech capabilities. (See also Microsoft Robotics Developer Studio microsoft.com/robotics ..)
I can add that Steve Prior [4] is a good person to ask about dialog systems in smart homes in general, and about his “Geekster Smarthome” [5] in particular.
[1] http://www.meta-guide.com/home-automation
[2] http://research.microsoft.com/en-us/projects/homeos
[3] http://www.kinectforwindows.org
[5] http://smarthome.geekster.com