"A multi-barrel machine gun with an extremely high rate of fire. Mechanoid-built."
The minigun is a Mechanoid weapon which can be found equipped by Centipedes. Although the Minigun has a very high rate of fire and a moderate warmup and cooldown time, it is generally impractical to use outside of point-blank to very close range combat (even with higher qualities) due to the insanely quick accuracy dropoff. A single centipede armed with a minigun is almost trivial to deal with if engaged at even medium range and behind a wall or sandbags, but stack up multiple miniguns with Inferno Cannons and Heavy Charge Blasters and things can quickly get out of hand without killzoning, (ideally at least 6) mortars or just outright raw firepower.
Due to the impracticality of having to be practically within melee range for a minigun to be effective, it's generally a better idea to either smelt a Minigun for a generous amount of Steel or sell it to suppliers who will pay a hefty amount of money for one. If you manage to get multiple miniguns to your name, you could possibly have a great deal of firepower on your side, but also a high risk of collateral damage if within your base dependent on setup. Their miss radius could also be an asset when it comes to crowd control in later game when there are many more enemies in raids.
As of Alpha 16, heavy mercenary raiders may be equipped with a minigun.