Commander Keen 1: Marooned on Mars is the first shareware game in the opening trilogy, Invasion of the Vorticons. You need to buy the other two episodes ("Commander Keen 2: The Earth Explodes" and "Commander Keen 3: Keen Must Die") of the trilogy if you want to play them. This first episode was one of the first side-scrolling games made for PC.
Billy Blaze, eight year-old genius, working diligently in his backyard clubhouse has created an interstellar starship from old soup cans, rubber cement and plastic tubing. While his folks are out on the town and the babysitter has fallen asleep, Billy travels into his backyard workshop, dons his brother's football helmet, and transforms into...
Commander Keen - Defender of Earth!
In this episode, aliens from the planet Vorticon VI find out about the eight year-old genius and plan his destruction. While Keen is out exploring the mountains of Mars, the Vorticons steal vital parts of his ship and take them to distant Martian cities! Can Keen recover all the pieces of his ship and repel the Vorticon invasion? Will he make it back before his parents get home? Stay tuned!
Keen's mission in this game is to find back the stolen parts of his ship. The evil Vorticons have stolen four objects from the ship and hidden them all in different places on Mars. Commander Keen's Megarocket was constructed from objects found around his house, which have been modified into starship parts. As a manual flight controller, he has used a joystick from his brother's video game. As for electricity, he has used a car battery from his mom's car. A heavily modified vacuum cleaner from their kitchen has been used as an ion propulsion unit. And as for fuel, he has used everclear from his dad's liquor cabinet.