Gravitar
Gravitar was released in 1982 by Atari. In this game, the player controlled a little spaceship through a series of planets. Planets were chosen at the start of the game from a map of the solar system, and choosing a planet took the player to a side view of that planet. Players will remember that gravity was a feature of this game, whereby the spacecraft was either drawn towards the planet surface or away from it depending on the level. Like Asteroids, there were five buttons to control the craft, including two to rotate the ship, one to shoot, one for the tractor beam/force field, and one to fire the thrusters.
Gameplay was relatively straightforward. The player was required to blow up red bunkers on the planets, and a main reactor, and when all the bunkers and the reactor was destroyed, if the player could escape in time, they would move onto a new planet, and when all planets were destroyed, the player would move on to a new solar system. The ship could be destroyed by running into terrain, getting blasted by one of the bunkers, or not getting away from an exploding reactor in time. The complexity of the planets, gravitational pull, and time limit to escape the reactor became increasingly more difficult as gameplay progressed.