A6 - Lighter, stiffer with less cushion. More ground feel. Same 4mm drop, and very close to the same fit as Kinvara. Feels very fast. The best shoe I've ever worn for racing or interval training.
Pureflow 3 - Heavier, softer, heelcup is much better, 4mm drop, fit is near the same. Less ground feel. Much prefered over kinvara 5 for long distance or recovery runs. I really love the toe box.
Newton DIII - Lighter, closer to A6, que's on awareness of form easily, feels fast, a little more of a sloppy fit in comparison to kinvara but a great shoe. 2-3mm drop, closer to transition to zero drop.
gobionic - zero drop, bigger toe box, closer to the ground with lots of ground feel but squishy soft landing. Weight is near the same. The newest gobionic has a 4mm insert making it even closer feel to the kinvara, but a different flavor. I actually prefer this shoe most for training and HM+ racing.
noteable mentions: Adidas Hagios 2, Adidas Takumi Sen, Go Run 3, NB 1400 v2, Mizuno Wave Ekiden