Zone 66 is a top down shooting video game released in 1993 by Epic Megagames. It uses 256-color VGA graphics and has sound cards support.
The story of Zone 66 happens two centuries into the future. The world is governed by The World Council which oversees all matters of a global scale. There are group of terrorists who don't like the idea of The World Council keep on fighting with the government armies, and the worst thing is the terrorists are in possession of nuclear weapon. Our mission is to destroy all of them to bring peace to the world.
The game involved controlling a number of aircraft over various landscapes destroying various targets.
The obvious difference between Zone 66 and other shoot'em up is it allow us to move in 360 degrees.
There are also a number of upgrades available for our ship. My favorite is the invincible mode that will leave a trail.
You can download Zone 66 here.