Chainsword from Space Marines 40k. Primary fire kills enemies instantly with a "burst" type fire enabling you to "swipe" at enemies for an area attack. Capable of killing 2 or 3 enemies in close proximity. Weapon has decent range for a "melee" type weapon. It is also capable of severing heads! It does significant damage to vehicles and titans if you can get close enough. I haven't tried but you should be able to sever the head of an unsuspecting rear hellbender turret gunner. There is also a mutator included to add this weapon to the default inventory while keeping all other weapon slots. It uses the same hot key as the impact hammer so you have to hit the button twice to bring it up or scroll through your weapons to find it.
Installation: Unzip the package and drop the files in the appropriate folders.