Alien Swarm is a top-down multiplayer shooter remade from the game mod for Unreal Tournament 2004. According to the main storyline, a group of troopers reaches the colonized planet occupied by the swarm of invasive aliens. They aim to search for survivors or, if needed, to destroy the colony to prevent the spread of hostile aliens. After finding no civilians alive, the group realizes that the only way out is planet devastation with a powerful nuclear bomb. The main gameplay idea is in completing levels in science-fictional locations and eliminating waves of Swarm aliens with all kinds of weapons to get new equipment and to unlock individual achievements. As the game is class-based, players are able to choose between 4 types: Officer, Special Weapons, Medic, and Tech. Each type has two characters with different abilities. The whole loadout can also be selected before starting the mission. The game is absolutely free-of-charge and offers both single and co-operative (up to 4 players) experience.