Alien

While there always was some evidence of the existence of alien life forms, it is very scarce. Until the events of the Fallout 3 add-on Mothership Zeta, there was no record of direct contact between humanity and the creatures.

The Brotherhood of Steel and Shi have encountered the bodies of alien life forms or their spaceships, as did the pre-War United States government, which kept its alien specimens mostly in Area 51. By extension, the Enclave and Brotherhood Outcasts also have access to alien technology; Alien Power Cells can be found at Fort Independence and in the armory of the Enclave's Mobile Base Crawler. They can also be found in the Citadel's armory (if you choose to destroy the Citadel during Who Dares Wins).

Finally being encountered in Mothership Zeta, they are small, greenish humanoids that are presented as malevolent creatures that seem to view humanity with contempt and will gladly vivisect their test subjects or keep them in cryogenic storage after torturing them for their scientific pursuits. The aliens themselves seem to have their own language and cannot be understood by the player in any way.

Crashed ships
Four alien ships are known to have crashed in the United States:


 * An alien ship in special encounter in California (Fallout).
 * Recon Craft Theta in Capital Wasteland (Fallout 3).
 * Another alien ship can explode over the head of the Lone Wanderer in the Capital Wasteland during a special encounter although the cause of the catastrophe is unknown (Fallout 3).
 * At the Citadel, there is information on a terminal (in the A-Ring) about another ship that crashed in a heavily wooded area that the government was not able to reach (Fallout 3).

Weapons
Firearms:
 * Alien Blaster
 * Firelance
 * Disintegrator
 * Alien Atomizer
 * Drone Cannon

Explosives:
 * Cryo Grenade

Melee weapons:
 * Shock Baton

Ammo:
 * Alien Power Cell
 * Alien Power Module

Robots and computers

 * Experimental Weapons Drone
 * Guardian Drone
 * Support Drone
 * According to its own (potentially unreliable) records, the Skynet computer was created based partly on alien technology. (Fallout 2)

Vehicles

 * Mothership Zeta - Large alien vehicle located in space near Earth dedicated to study of humanity.
 * Recon Craft Theta - Small alien vehicle, found in Capital Wasteland. Used by 1 pilot.
 * The Second Mothership - A ship of the same design as Mothership Zeta, it comes right after Mothership Zeta's Bridge is captured by Lone Wanderer.
 * Crashed saucer in California (probably non-canon) - A small vehicle that housed 2 pilots.

Other

 * Alien Epoxy - Alien repairing agent.
 * Personal protecting shield technology

Appearances
Crashed alien ships and alien dead bodies appear in Fallout and Fallout 3. The Alien Blaster appears in all three games. Aliens themselves appear and abduct the player in the Fallout 3 add-on, Mothership Zeta.