Auger from Resistance series. A heavy energy weapon, that gives the user wallhacks and its shots pass through anything non-organic. It also has the secondary ability of deploying a shield, that deflects anything, except its own ammo.
Bullseye from the same series was also fun. It was an aimbot gun. Tag enemy once with its secondary homing shot and after that all the shots homed in on the target. Additionally, if you shot the homing tag on a wall or ground, it would create a weird trap, where all the shots fired at it semi-orbited around the tag, waiting for someone to stumble on it or exploding like a sharpnel mine, when you undid the homing tag.
That series had a lot of innovative and fun to use weapons.