No revenue estimate for GOG — its rating/review counts don't calibrate to sales the way Steam's do. The Steam version is estimated at $553.6K — a different platform, not this one.

X-Com: UFO Defense

You are in control of X-COM: an organization formed by the world's governments to fight the ever-increasing alien menace. Command deadly close-combat battles  Shooting down UFOs is just the beginning: you must then lead a squad of heavily-armed soldiers across different terrains as they investigate the UFO crash site. Tackle the aliens with automatic rifles, rocket launchers, and even tanks in the struggle to retrieve useful technology, weapons or life forms.  Research and manufacture alien technologies  Successful ground assault missions will allow X-COM scientists to analyze alien items. Each new breakthrough brings you a little closer to understanding the technology and culture of the alien races. Once you have sufficient research data on the UFO's superior weapons and crafts, you'll be able to manufacture weapons of equal capability.  Develop a strategy to save the Earth  You must make every crucial decision as you combat the powerful alien forces. But you'll also need to watch the world political situation: governments may be forced into secret pacts with the aliens and then begin to reduce X-COM funding.