Assault rifle (Doom)
The rifle was a weapon in the pre-release versions of Doom, an implementation of Tom Hall's initial Doom Bible idea for a "machine pistol" with a knife attachment. Presumably intended to be the player's starting weapon, it was replaced with the pistol in the Doom press release beta and does not appear as a usable weapon in final versions. The player character and trooper sprites still depict them wielding rifles, however.
Additionally, the rifle was to accept the bayonet as an attachment, which would serve as the basic melee attack. This feature also did not make it into the final releases, being replaced by the spiked knuckleduster.