The latest entry in the long-running Call of Duty franchise, Call of Duty: Infinite Warfare, is currently in a free-weekend state. But only the multiplayer of the game can be played during this event; campaign and zombie mode is not available for free. This event ends on Sunday, February 26, at 10AM PT/1PM ET.
You can get the game from Steam.
The game is currently being sold at a 50% discount on Steam. And in case you buy the game after trying it during the free weekend, all your progress will be carried over to the full version.