Steam offers downloads of the Call of Duty: Black Ops 3 Multiplayer DLC Trial Pack for Windows for free. (You must currently own the base game to get it.) This DLC gives players access to all multiplayer features and maps found in the game's four DLC packs. (Players who already own this DLC will instead receive an XP bonus while playing.) The trial ends June 29.
Note: This trial DLC will automatically download to your PC. Players can opt out of the trail here.