So far the only way I've found to take people down without killing them is Sleep Darts. None of my skills (that I've noticed) seem to be able to knock people out/put them to sleep. I noticed the "parry" button is also "choke" but when sneaking up on someone and pressing parry I just block, I don't seem to choke them; I'm also unsure whether that's lethal or not.
What are all the ways to knock someone unconscious? There seem to be very few.