This one looks promising too, although very early days. https://github.com/srvk/eesen
I think we'll see something state of the art (that runs on mobile devices pretty soon in the open source world.
You also need a good microphone setup to get good quality speech in.
Both Echo and Dot have a 7 mic array with beamforming, which helps a lot with far field speech recognition.
There are a few open source alternative, Kaldi is new to me