The real-time strategy/first-person action game hybrid BattleZone: Combat Commander, which builds upon the legacy of the 1998 game BattleZone, will have its multiplayer portion free to play until Monday, July 30th at 10 AM PDT. To access it, simply install the game through the Steam client or GOG Galaxy (not supported on the GOG offline installers due to the nature of the multiplayer aspect) and play it.

You can find more information on the game on the official website.