Md520n/md600n/md902n
Simple and effective system that just about eliminates pedal input to compensate for collective changes. I remember when first came across it - actually in a demo video from MD - and the test pilot stabilized a hover, took his feet off the pedals and yanked the collective all the way up (to the red of the tq-meter). No yaw...
I have since flown the MD900N (once) and really liked the system. It works.