Atomaders 

This space-shooter is based upon the classical Invaders/Galaxian idea. You have to liberate your planet system from the alien invasion using your spacefighter. Player can obtain various extra-weapons and special abilities by destroying enemy cyborgs, fighters and motherships. Each planet has its own cyborg types and an unique powerful boss at the last level.Atomaders is a slow and old fashioned shoot-em-up game, it presents a basic interface with decent graphics and sounds. It is identical to those Arcade Games where you had to shoot at battle formations of enemy aliens.

With the help of a space-fighter you have to prevent an alien force from attacking the Earth. The objective is to shoot and destroy as many aliens as you can, and avoid their bullets and missiles. While playing, you will find some power-ups like bullet shields and as you get to pass levels, aliens get faster.

The basic idea might be fun but is not well developed (this is an old program), so if you enjoy simple arcades I recommend Alien Sky from the same developer instead.

It starts too slow, and ends up too fast, there is not much control of the movement, so you might feel frustrated, I don't recommend it, but if you feel curious, a 60 minutes trial is available for download so you can decide if you want to buy it or not.

It is compatible with Windows 95/98/ME/2000/XP, there are not versions available for Mac.