: This is the most popular client. It provides dedicated servers, anti-cheat, and custom content. While it is a free service, you generally need the base game files to run it.

: Another community alternative that allows for multiplayer with bots and offline Zombies mode. 3. Important Security & Safety Warning

If you are looking for "free" options, the PC community often uses third-party clients. These do not require the official Steam version and provide better security for multiplayer than the aging official servers.