You know what Fallout: New Vegas needs? More dismemberment. There's already a mod that will have NPCs' legs and arms flying every which way, and now another modder has handed players the perfect weapon for the job: Dead Space's plasma cutter. The creator says it's "not intended to be an exact copy", but it will flip between horizontal and vertical firing modes just like the one that Isaac Clarke uses.
In its vertical alignment, it fires three laser beam projectiles that deal 13 damage each and collectively use two energy cells. Switch to a horizontal setup and it'll instead send out a single blade of energy that uses five energy cells to deal 50 damage.
Naturally, it does more damage when you aim for the limbs, and you can modify it to increase its stopping power or capacity. After you install the mod, you'll find the weapon in the medical wing of Vault 34, and you'll need a repair skill of 40 and a science skill of 65 to get hold of it.
It needs a couple of other mods installed for it to run properly—you can read about them on its Nexus page—and it's recommended that you use it with another mod called Live Dismemberment, which was the inspiration for adding the plasma cutter in the first place. That mod lets you blow limbs off human characters, and if they lose a leg they'll pull themselves along the ground with their hands. Brutal.
Below is an image of the horizontal configuration of the plasma cutter, and the vertical firing mode is at the top of this post. I like the look of the vertical one more, but firing a sweeping arc of energy sounds like fun.