Cyberdog

Cyberdog is a generic term for any dog that has been modified robotically. For some dogs, such as Robodog of NCR's Dr. Henry, the modifications are basically physical modifications, such as robotic enhancements to limbs. Others, such as K-9 of Navarro's Dr. Schreber, are more extensively modified, with enhancements to the brain and vocal organs allowing intelligence and speech.

Fallout: New Vegas
There is a cyberdog companion in Fallout: New Vegas called Rex

Rex is a faily decent companion granting a perk which alows the PC to see items while zoomed in without a weapon. The items will be highlighted green. Rex has a low DT and can be downed quickly

Achieved
In Fallout 2, one may be obtained at the New California Republic if you inject a super mutant of your choosing with a sort of chemical that supposedly stops genetic damage. This quest is received from a scientist, and after you report your results back to him he will reward you with Robodog.

Appearances in games
Cyberdogs appear in Fallout 2 and Fallout: New Vegas.