Pretty much this adds a door in Megaton (Yes it is so amazingly obvious) right next the the atom bomb. This magical door teleports you to my Development zone. Basically there are crazy weapons, floating corpses, exploding refrigerators, weapons test NPCs (Leave and come back and they respawn)

List of weapons:

Grenade launcher (Use With Caution)
Basically what a grenade launcher would do if it was fully automatic.

Liberty Prime's Lazer.

Dev Sniper Rifle
Shoots a ballistic missile with amazing accuracy.

Insane knife launcher V1
This launches knives at your enemy in slow motion. It's pretty funny to watch a wall of knives ram your enemy at 2mph.

Insane Knife Launcher V2
Basically launches knives at 500mph fully automatic.

Flame Shield
This... Is odd. All it does is keeps a cone of infinite flame at wherever you shoot it. So pretty much... Yeaahh..

Flame Sphere
Catches everything around you on fire pretty much.

Boulder Launcher
Just... Don't even ask.

Dog Launcher
By FAR the funniest. Launches dogs, rapidly might I add, at your enemy. (Barely any damage)

The "I don't even know"
Legit, I just didn't know what else to call this monstrosity... It spawns a barking dog that lasts for 30 seconds. (Mid air)

The Lover Maker
Failed experiment
It launches a rocket ship at your enemy.

MIRV pistol
Lobs a MASSIVE missile into the air, very much like how a normal mortar would fly. Very fun.

I may have missed some, but whatever.

Next:

The "Do not shoot" refrigerators.
Shoot them and they kill you. They use the Satcom nuke strike. You will not survive.