The webspeech api is web based, which I think goes to Google if you're using Chrome or Firefox. It also has a fairly long lag (well over a second?) and is mostly suited to text dictation.
In that case I think the headline “open source voice typing” is not a good description. I would expect it to work locally with a headline like that. Not to ship off all of my voice data to Google and have them run the speech to text stuff.