There are two ways that you can play Call of Duty for free, and they're both dramatically popular. Firstly, there's the Warzone ecosystem, which is made up of Call of Duty Warzone and Call of Duty Warzone 2.0.
Featured in Call of Duty: World at War, Call of Duty: Black Ops, Call of Duty: Modern Warfare 3, Call of Duty: Black Ops II, Call of Duty: Black Ops Cold War and Call of Duty: Vanguard is a hardcore version of Free-for-All.