Slot 1:
Fists
Primary Fire is regular jabs, Alt-fire is an uppercut that always flinches enemies.
Chainsaw spawns are instead an upgrade for your hands, which improves your primary fire into a full-blown combo that stunlocks enemies.
Berserk packs will drastically beef up your melee attacks and can stack over the melee upgrade, allowing you to literally send enemies flying, or obliterate enemies with lightning fast punches.
Slot 2:
Plasma Pistol
Starting pistol with infinite ammo. Primary fire is low recoil weak shots, alt-fire is more powerful high recoil shots. Both can be mashed for a higher firerate, but only the primary fire can be held down for sustained fire.
Slot 3:
Mars Streetsweeper Assault Shotgun
A semi-automatic bullpup shotgun, with a tight spread and solid damage. Primary fire is a single shot, alt-fire is a quick burst that can reliably delete revenants.
Decimator Flak-Shotgun
A pump-action shotgun that fires ripping bouncing super-heated flak. Primary fire is a blast of flak, while the alt-fire is a large arcing slug that explodes on impact into regular flak on hit, rewarding precision with high damage.
Slot 4:
VoidRipper SMG
An SMG with a high rate of fire and a larger magazine to compensate. The primary fire is standard full-auto with noticeable but controllable recoil, with the alt-fire being a fuller-auto that dumps the entire mag in seconds. Be warned, for while the alt-fire can easily shred an archvile, it can't be canceled once it's started.
LongBow Pulse Carbine
A hybrid energy-based Carbine, suitable for combat at mid to long range. Primary fire is a burst fire with a quick cyclic rate, with the alt-fire being a powerful ripper sniper projectile that can obliterate large bodied enemies with ease.
Slot 5:
Techbase Demolisher Assault Launcher
An assault rocket launcher that fires micro-missiles from a drum mag. Similar to the Assault Shotgun (but with rockets), Primary fire is a single rocket, with the alt-fire being a quick burst, suitable for quickly dealing with higher tier demons.
Collateral Damage Frag Shotgun
A hit-scan explosive shotgun.
Need I say more? The primary fire is a single shot with a wider spread than the other shotguns, but is compensated for due to the shotgun being loaded with explosive shells. The alt-fire chambers two extra shells, resulting in a blast that fires 3 times the pellets, resulting in devastation for any demon unlucky enough to be in your sights.
Oh, and the splash damage from this shotgun affects boss tier enemies. 
Slot 6:
RailHawk Plasma Lance
An explosive plasma DMR meant for longer range engagements. The regular fire rips through enemies and explodes upon impact with a surface, and the alt-fire is a projectile that instead explodes on impact, and has a much bigger discharge.
Neither plasma explosion harms the player, so feel free to fire this at your feet when surrounded by demons.
Legion Gauss Chaingun
A prototype chaingun designed to fire gauss projectiles similar to a railgun, that also doesn't need to reload. The regular fire is a fully automatic stream of weaker piercing projectiles, while the alt-fire fires every barrel at once, resulting in a 6-projectile shotgun-esque blast.
Slot 7:
While Slot 7 ammo is relatively rare, both Slot 7 weapons can and will invalidate even the most challenging encounters.
Chaos Wheel
A revolver heavily modified to fire from a small BFG reactor. The primary fire is a slower, more controllable single small BFG projectile, that when mashed turns into fan-fired shots that trades higher recoil for a firerate as fast as your trigger finger. The alt-fire is a powerful blast that fires multiple small BFG projectiles at once. Reliably removes bosses from existence when fired up close.
YEEHAW, SPACE COWBOY.
Room-Clearer 6700
A BFG specially modified to fire a BFG Ball......that spits out dozens of smaller, bouncing BFG Balls. True to it's name, the primary fire of this man-portable war machine fires off a BFG ball that fires smaller BFG balls.
Protip, longer flight time equals more BFG balls. The alt-fire is a scaled down, single BFG ball for when you simply need some breathing room and don't need to cleanse your entire area code of demons.
Sidenote:
The Assault Shotgun, SMG and Pulse Carbine all use CustomInventory for their pickups to give them a random chance of scavenging ammo if you already have the weapon. This was done to ensure pistol starts are still doable, but prevent the player from drowning in ammo since they all utilize mag based reloads, since every shotgunner or chaingunner would drop wayyy too much ammo.
