A hard but still a fun retro Space Invaders game
Galacta, like the similarly named games Galaxian and Galaga, is an arcade-type shoot-em-up game where you move your ship back and forth on the bottom of the screen, and things come down from the top to attack you.
Galacta uses the keyboard to move the ship left and right, and the CTRL key to fire. It runs in DOS mode just fine under Windows. The game is so old, it uses the PC speaker for sounds. But it's still lots of fun.
And don't try to register it, the info inside the file is old and outdated.