This is a Fortis Manufacturing, Inc. Vertical Foregrip known as the Shift, model SHIFT-HNDSTP-ML-CF. 

Fortis Manufacturing's Shift Angled AR Fore Grip integrates form with functionality. The Shift is a hybrid of sorts. The shape works as a comfortable hand stop when going with the thumb over method. The grip allows you to handle the weapon with the confidence and the organic design enables the operator to manipulate the rifle in ways that's not quite possible with other vertical grip designs. Keep your speed and accuracy up. Put more down range and on target. 

Features: 

M-Lok Mount