This is a Magpul Industries Grip known as the MOE Slim Line Grip, model MAG539-FDE.
Similar to the MOE-K2" the MOE SL Grip (MOE Slim Line) is a drop-in upgrade for AR15/M4 pistol grips with a more vertical grip angle optimized for short LOP weapons that bring the primary hand in closer to the shooter's body. With an aggressive TSP texture for positive weapon control along with excellent ergonomics" the SL Grip provides a slightly smaller size and slimline feel. All mounting hardware included. Made in U.S.A.
Features:
Replacement for AR15/M4 pistol-grip
More vertical grip angle than standard A2 grips
Slimmer thickness for a slightly smaller feel