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 $193.1K — a different platform, not this one.

MDK

As vast alien mining cities suck the power and minerals from every major metropolis on Earth simultaneously, time is of the essence as millions of civilians are expiring by the second. Using your stealth parachute and the now infamous "Zooming" head-mounted sniper weapon, your task is to slip in undetected from the sky, seek out and remove the alien leader by any means. Fully reactive “smart enemies” think, listen and communicate in a calculated assault on your life. Think fast and act faster against the most sophisticated artificial enemy intelligence of its time. The main objective of the game is to basically shoot everything that moves and everything means every alien you will come across. The one and only way to stop the alien invasion is to kill'em all by any means necessary, such as the smallest nuclear bomb, surfboard-like jet or bomber plane. Your goal is simple - repulse the alien invasion and save the Earth... almost single handedly. One of the greatest and most memorable action games of all time Fun and addictive gameplay, filled with humor - a trademark of games by Shiny Entertainment To this day no one really knows what “MDK” actually stands for...