What experimental armors can you discover in the Proving Grounds

There are 7 possible mods, and all weapon mods have 3 levels - basic (no prefix), advanced, and superior. Bonuses listed as x/y/z correspond to those 3 levels.

• Stock - 1/2/3 Guaranteed damage on a miss.
• Auto-Loader - 1/2/3 Free Reloads per mission. (Reloading doesn't cost an action)
• Extended Magazine - 1/2/3 extra ammunition before reloading.
• Repeater - 5/10/15 percent chance to instantly kill an enemy, regardless of remaining health. ("Executed" text will pop up when this triggers)
• Scope - 5/10/15 Aim bonus when using the upgraded weapon. 10/15/20 Aim bonus when using the upgraded weapon against targets not in cover. (Does not apply to secondaries)
• Laser Sight - 5/10/15 Crit chance when using the upgraded weapon. (Does not apply to secondaries)
• Hair trigger - 5/10/15 percent chance for each shot to not use an action.

There are 5 types of Experimental Ammo, and 3 types of Experimental grenades.

Ammo

As a side note, Ammo applies to Sharpshooter pistol shots.

• Armor Piercing - Bypasses an enemy's armor. No bonuses against enemies without armor.
• Dragon Rounds - Passive bonus damage and a chance to light targets on fire. (Enemies immune to fire can't be lit on fire, but still take the bonus damage)
• Talon Rounds - Reaper Rounds' big brother! +20% passive crit, and an extra +1 damage on critical hits. No extra range penalties like its predecessor.
• Tracer Rounds - +10 Aim while equipped.
• Venom Rounds - Passive bonus damage and a chance to poison the target. (Enemies immune to poison, like Chyrssalids, still take the bonus damage)

Grenades

• Acid Grenade / Bomb - Shreds more armor than a frag grenade, applies Acid to those hit, and leaves acid terrain tiles on the map for a few turns.
• Gas Grenade / Bomb - Larger area grenade that deals damage and poisons enemies hit.
• Incendiary Grenade / Bomb - High damage and sets enemies on fire.

And, though you didn't ask for it, why not --

Heavy Weapons

Heavy weapons are tiered. The "Heavy Weapons" become available once you unlock the E.X.O. suit, and the "Powered Weapons" become available once you unlok the W.A.R. suit.

Heavy Weapons

• Rocket Launcher - Unlocked by default. Deals explosion damage in an area & shreds armor.
• Flamethrower - Cone of flame to deal damage and ignite enemies.
• Shredder Gun - Cone of bullets to shred armor and cover.
• Blaster Launcher - Powered Weapon. Upgraded Rocket Launcher.
• Hellfire Projector - Powered Weapon. Upgraded Flamethrower.
• Shredstorm Cannon - Powered Weapon. Upgraded Shredder Gun.
• Plasma Blaster - Powerd Weapon. Linear area damage.

Here's an imgur album assembled by SYLOH with the in-game descriptions.