Xenonauts is described as '1 October, 1979: Unidentified forces presumed of extraterrestrial origin arrive in Earth orbit. Panic spreads across the globe as attempts at communication fail and attempts to engage the invaders are met with heavy losses and little success' and is a Turn Based game in the games category. There are more than 10 games similar to Xenonauts for a variety of platforms, including Windows, Steam, GOG.com, Linux and Mac apps. The best Xenonauts alternative is X-COM. It's not free, so if you're looking for a free alternative, you could try Fire Emblem or UFO: Alien Invasion. Other Xenonauts like games are Othercide, Into the Breach, Valkyria Chronicles and Shadowrun Returns.