The Laser Chainsaw is a scrapped Duke Nukem 3D weapon.
According to its concept art, the Laser Chainsaw would be a powerful beam sword. When actvated, a siren would flash.
The art also gives a look into the weapon’s power. It says that the blade from the Laser Chainsaw would “sever immediately”, which would make it very powerful if it was put into the game.
The Laser Chainsaw itself was scrapped, but the design for the weapon was recycled for the Flamethrower, which then became the Freezethrower at the last minute. The Duke Nukem Forever incarnation of the Freezethrower retains many elements from the Laser Chainsaw in its design, such as the siren and the grip.