Forgotten Worlds is a coin-op created by Capcom in 1988. The home computer versions were developed by Arc Developments and published by US Gold in 1989.
The game supports simultaneous 2-players mode, but the arcade had particular controllers. Something that you can't find on any home computer or console. Thetwo2 heroes can rotate their guns, like in Contra, but they can also fly with a jet-pack, making it very complex to control the game with just one joystick.
The graphics are great, but it's not the most accessible game out there.
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Download for Mac