In 2177, SCIENTISTS made contact with an ALIEN species. But it was soon discovered that these aliens were not benevolent. They brought society to the brink of extinction. Only one man can save the human race. That man's name is CHRIS GUNNARSON. Take control of CG and save the human race.
Use WASD to move around. Press K to jump/submit and L to shoot. Press ESC in a menu to cancel. Press Left Shift to duck. You can duck and shoot at the same time.
For Mac users, unzip the file, then right click on the app, then click open. You'll get a warning about an untrusted executable. That is because this executable is not on the App Store. Click open again. Now the game starts. You only have to do this once, after this you can double click the app icon like you would open other apps.