Twitch's gadget the Shock Drone. The Shock Drone can shoot a taser which is able to either destroy or disable defender gadgets.
Montagne's gadget is his primary weapon which is a shield. The shield is able to extend so it can cover his feet while standing straight up. The shield extends over his sides and head to a certain degree. You can extend or retract the shield as many times as you want and anytime you want.
Doc's gadget is the Stim Pistol. The Stim Pistol is able to revive downed but not out (DBNO) teammates or heals someone 40 HP. It's also able to over heal, so for example if you are at 100 HP and get a stim shot, you will be a 140 HP (and it will slowly go back down to 100 over time). Doc can pick himself back up if he is in the DBNO state. Doc has 3 stim shots.
Rook's gadget is his armor pack. The armor pack contains five armor plates, one for each teammate including himself. The armor plates make it so that you will always be DBNO instead of dying straight away. Rook has one armor pack.