Citizen Abel: Gravity Bone is a total conversion of Quake II playable as a standalone game. It is a follow-up to the four Citizen Abel missions made for Quake II released between August 1999 and August 2001 by the same author.

In this game the player is Citizen Abel, the most efficient and economical hit-man in the galaxy. He is contracted by an employer to perform and complete various missions. The game removes all references to the original Q2 engine with its brown colours by presenting a bright, lush environment with bloom, populated by blockheaded figures. The game contains two missions where the player needs to complete a contract, followed by an extensive ending.

The game is played like a regular shooter, with the keyboard keys to move and the mouse to aim, although no weapons need to be fired. In the first mission Citizen Abel needs to become a waiter and deliverer a manitoba beast bug in a wine glass to a certain guest at a party. In the second mission five birds need to be photographed. Various tools are used, such as hammer, spray cans, a photo camera and more, along with some jumping puzzles.

More of the story is told through flashbacks and at the end of a completed contract, a Portal-like overview of the mission is shown.

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