Scum of the Universe is a space trading game that combines two genres: arcade and strategy. On one side, it's a classic vertical-scrolling space shooter game. On the other side, it is an adventure and strategy. You should choose whether you'll be an independent space trader, firearms smuggler, fierce freedom-fighter or something in between.
Following the main storyline, you go through the galaxy from one planet to another. Space travel requires fuel, so you need to keep earning money to buy it. You can also buy various upgrades for your spaceship and weapons that affect the arcade part of the game. The storyline itself is not linear. There are also some points where you'll need to make decisions that will determine your destiny.
For thousands of years, people of planet Xen have colonized the planets in their galaxy. As time went by, many colonies grew unhappy about their status, as everything was controlled by Xen. Some of them organized military units and declared independence. You can see the status of each planet by "Rebel Sentiment" indicator. Planets with RS higher than 50% are ruled by the Rebel government, and Rebel laws apply.
Trading firearms is legal on planets ruled by Rebels, as they need as much firepower as they can get. On the other hand, Empire forbid all the trading with firearms and other ground weaponry as they wish to maintain their military advantage. One of the ways to make a lot of money is to buy cheap guns at Empire planets and sell them for a lot of money on Rebel planets where demand is extremely high. But be careful as you'll need to fight Empire fleet once they find out you're a smuggler.
Beside the raging war between Xen Empire and the rebels there is increased activity of alien species, who destroy human ships. The stronger alien activity, the more waves of alien ships you'll need to defeat in each planet's outer orbit. Some of the aliens you destroy may drop artifacts (big blue ones) which you can sell at any space station for 20credits a piece.