Zombo

Zombo is a completely unofficial, not-for-profit fan-game by Malcolm Kirk.

You must rescue 6 survivors and defeat the secret end of game baddy to win. Colour coded keys are scattered around the planet, as are several other items, some of which may help, others of which may not, but there's a gun somewhere which'll probably come in handy. However, please bear in mind that the Shootybang 2000 can only fire horizontally. To fire vertically, you'd require an upgrade to the Shootybang 3000 and that's not available to you within this game.