It's called "Nemesis - Unlimited Skyrim Behavior Engine"
made by ShikyoKira (same person that made ultimate dodge)
It's still in BETA, for SSE and Legendary
So far it supports
Every animation type that FNIS does (and supposedly more)
No hard limit on animations (current 21k)
Pros over FNIS:
Much larger animation amount (right now running over 20k- (bilyy/anub/leito/nibbles/MNC/), I don't CTD like I used to when using