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.
Here's a couple gameplay images. It's a fun game!
Swarms of flapping birds descend on you, dropping bombs all the while. I've got my shield activated (you collect shield power-ups and use them at will), which is good, because otherwise i would be DEAD in half a second.
In between groups of enemies (usually 3 waves of 3 different enemies), you have to traverse a rock-strewn asteroid belt. If you shoot the rocks, sometimes they'll release gold ore, which are big points.
These guys are fun. Shoot a grey box, it explodes into three orange boxes, which inturn explode into three red boxes. You COULD just let them go by, but that's no fun. And no points, either.
Aheh-heh-heh. Ow. These guys are nasty.
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And don't try to register it, the info inside the file is old and outdated.