If you're looking for a shooter game available both on Mac and Linux, you should try Half-Life 2. Besides PC, it was released for PlayStation and Xbox, and for Windows it's available on Steam.
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{"name": "Half-Life 2", "genres": "shooter", "platforms": "PlayStation, Xbox, PC", "available_on_steam": "yes", "has_linux_release": "yes", "has_mac_release": "yes", "intention": "inform"}
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