Pocketsphinx[1]. I used it, and pico2wave along with some old-school interactive-fiction style code to create a "computer" for my open source space game[2] so I can drive the spaceship around by talking to it[3][4].

[1]https://cmusphinx.github.io/wiki/tutorialpocketsphinx/ [2]https://spacenerdsinspace.com [3]https://www.youtube.com/watch?v=tfcme7maygw [4]https://scaryreasoner.wordpress.com/2016/05/14/speech-recogn...