Comment by iamsrp

I wrote a toy one which works well enough for me:

  https://github.com/iamsrp/dexter

It'll run on a cheap Ubuntu box if you can't get a Pi.

And lots of people seem to like Rhasspy too:

  https://github.com/rhasspy/rhasspy

which does rather look more polished than my efforts (though I've not tried it myself).