Survive for as long as possible. Use the arrow keys to move and the space key to fire your gun. If you pick up a gun that you don't like, press the 'x' key. Press the 'z' key to equip your knife. To reduce lag, start the game, get to the actual playing part, shoot a zombie, and then double click the green flag. "It's a post apocalyptic future, and you, Marco, have been deployed to eliminate infected life from a collection of varied locations. Occasionally, you will get help in the form of weapon crates or care boxes, but other than that, you're alone in your fight against the undead. Lock and load, this ain't gunna be easy..."
Made back in 2013, I think. To this day it's one of my favourite projects I made. Made on Scratch 1.4.