Ask HN: What technology do commercial jets have for avoiding collisions?

With the horrible news this morning about the American airlines collision with a helicopter near Washington DC, I am sure the biggest focus will be on how these two aircraft came to be perilously close together, but I am also wondering: Does anyone here know the state of collision avoidance technology in commercial airplanes? This is something that cars are starting to get pretty good at, at least fancy ones like Teslas (I know they make mistakes they still do an impressive job of detecting potential collisions and avoiding them). I imagine that this is a harder problem for planes.