Enemy Unknown

This game is made by Microprose. They realesed it in 1994.
UFO is one of my all time favorites. The game puts You in
role of head commander of UFO, Terran special forces unit
specialized for fighting the aliens. You can build bases,
research new equipment and alien technologies, fight aliens
on ground and in air, defend civilians in cities, attack
alien bases... The combat mode is the one that made this game
so popular - You get to control Your squad in turn-based combat.
To see this and a whole lot more download the game and play it!