A gravity gun is a type of device in video games, particularly first-person shooters using physics engines, whereby players can directly manipulate objects in the world, often allowing them to be used as projectiles against hostile characters. The concept was popularized by the gravity gun found in Valve's Half-Life 2, as well as the Temporal Uplink found in Free Radical Design's TimeSplitters: Future Perfect; although a similar concept was used by id Software during the production of the earlier game Doom 3, eventually leading to the introduction of a physics-based weapon in the expansion pack Resurrection of Evil. Later games, such as Portal, BioShock, Crysis, and Dead Space, have been influenced by the success of these physics-based weapons, adopting their own styles of comparable abilities or weapons.