Xtron

Xtron is a Space Invaders game, and mixed are some elements from Galaxian.

The player's ship is bound to the lower border and is able to move left and right. At the beginning of each level, all alien ships are approaching the screen in different formations, already firing at the player before they settle to their position on the top of the screen and start single attacks to below.

After every two stages new alien types are appearing. There are no extra weapons and the player ship is limited to very few projectiles at the same time. The background is a scrolling starfield, the user interface is only an optical gimmick beside display of points and players lives.