I have been mainly involved in speech recognition in the nineties when Lernout and Hauspie was the market leader. They went bankrupt and the speech technology was bought by Nuance Communications. They have Linux solutions, but I'm almost sure no free/opensource versions.
Most of the searching I did turned up works in progress. More or less contributing your own voice input to the projects so they can improve on it. I guess it will be a couple of years before there is a usable OS version.