In Space War, two players attempt to destroy each other while flying around a planet with a strong gravitational pull. The planet is a rarity: it is a gas giant so near a sun that it radiates energy. The ships use this energy as their power supply, and for this reason are forced to fly perilously close to the planet at all times, constantly struggling with the planet's gravity for control. Actually colliding with the planet, or straying too far away, is instant death.

Each player controls a ship via four keys. The blue player, who is on the left, uses the 'a', 's', 'd', and 'w' keys. The 'a' and 'd' keys rotate the ship, and the 's' key thrusts. The 'w' key fires a torpedo. The torpedoes are affected by gravity but because they are fast projectiles the effect is very slight. The red player, who is on the right, uses the 'j', 'k', 'l', and 'i' keys. If the players are playing on a keyboard where key presses can lock the other player out some courtesy is necessary to enjoy the game.

Space War was reportedly the first video game ever written, designed originally with the classic cartoon rocket-ship look on a vector graphics terminal. By the light of the green phosphorous some of the earliest and most famous names in the computer industry played a game very similar to this one.