The weapons in .kkrieger have not been named, so the easiest way to reference them is by the key used to equip the weapon (as well as describe it).
The initial weapon you begin with, this rifle-like weapon shoots a slow arcing projectile. Although the firepower of this weapon is terrible, you'll soon find the next weapon will supersede its usage.
The upgrade of the basic rifle, you can hold down to fire shots rapidly, which is great against the larger enemies in the game. When attacking the basic, four legged walker you should tap the button twice so you don't waste ammo. However, it's automatic fire is just as fun to use in dealing with a large number of targets.
This is located in the first section, just behind the first door you need to open.
The third weapon is another rifle, except this time the arc of the projectiles is greater. This deals twice as much damage as the basic rifle, but cannot be fired quickly.
You can find this at the start of the fourth section, after coming from a large arena where you dealt with two medium walkers.
The first launcher weapon, it fires a slow arcing explosive projectile. Be careful with this weapon, as you can injure yourself with the splash effect.
You can find it in the second section after the turning corridor, and will see it in the far right corner. Even though it is the third weapon you discover, it occupies the fourth weapon slot.
The second launcher weapon, it uses different ammo (although the ammo itself looks the same) than the first launcher, yet it performs just like the other. The main difference between the two is the design of the gun.
This is located near the end of the game, when you start climbing the large, straight staircase located after the white corridor.