Sabotage is a 1981 computer game for the Apple II family of computers, written by Mark Allen and published by On-Line Systems.
The player controls a gun turret at the bottom of the screen by either keyboard, paddle control, or a single axis of a joystick. The turret can swivel to cover a large area of the screen, but cannot move from its base. Helicopters fly across the screen at varying heights, progressively lower over time, dropping paratroopers. The gun may fire multiple shots at once, and the shots may destroy helicopters or shoot paratroopers. Optionally the gun can also control its shots after they are fired (an initial game setting).
Paratroopers may be disintegrated by a direct hit, or their parachutes may be shot, in which case they will plummet to earth (splattering and dying if they were sufficiently high when the shot hit, scoring on impact). If they land on a previously landed paratrooper, that paratrooper is also killed. If a falling paratrooper collides with another paratrooper in the air, the lower paratrooper loses his parachute and falls (occasionally two paratroopers from different helicopters can collide causing only the lower one to fall to his death). Furthermore, destroyed helicopters turn into shrapnel, which may destroy other helicopters, paratroopers, or parachutes. Periodically, jets may fly by and drop bombs; the jets may be shot as well, but the bombs must be shot as they unerringly home in on your turret.
Waves consist of helicopters coming at progressively lower altitudes, a brief rest, then a wave of jets. If the jet wave is survived, there is a short respite, then the next round of helicopters begins with an extra row of helicopters on the first run. The next jet wave also has an extra row of jets and the potential of having bombs dropping from two directions. Paratroopers will not deploy their parachutes until they drop below the last row of flying helicopters.
The player earns points by shooting helicopters (5 points), paratroopers (2 points), jets (5 points), and bombs (25 points). Firing a shell costs the player one point, so if one is playing for score, there is an incentive to conserve ammo. The score never drops below zero.
The game ends when the player's turret is hit by a bomb, when a single paratrooper lands directly on the turret base, when three paratroopers safely land atop each other immediately adjacent to the turret base (allowing the third to jump onto the base), or when four paratroopers safely land on either the left or right of the turret (that is four on one side, not four total). If four land on a side, they are able to build a human pyramid and climb up to the turret and blow it up once the sky is clear. There is a chance to kill the paratroopers before they assault the turret if you can cause still-airborne paratroopers to fall without parachutes on enough ground forces to reduce them to fewer than four on a side, fewer than three stacked by the turret base, or remove all from atop the base. They will not perform the final assault until all airborne forces are gone.
Source: Wikipedia, "http://en.wikipedia.org/wiki/Sabotage_%28video_game%29," available under the CC-BY-SA License.