Quoted from Borderlands Wiki
E-Tech guns are a new type of weapon featured in Borderlands 2. They are weapons that have been upgraded with Eridian technology, and replace the Eridian weapons of the first game. Though they can be found almost anywhere, they are relatively rare loot, and color-rated as magenta rather than the rare purple. The component that determines whether a weapon is E-Tech is the barrel; E-Tech weapons have special barrels with hexagonal petal-like structures with glowing interiors, which open out as they fire.
All E-Tech weapons shoot standard ammunition in a variety of different forms, ranging from lasers to energy balls to slow projectiles that ricochet. E-Tech weapons almost always use multiple rounds of ammunition per shot, and usually have low muzzle velocity for their type but high damage. They are rare drops from standard chests, but are common finds in the Sanctuary loot chest. They will always have their manufacturer's highest-quality (purple) skin.
E-Tech is introduced in Dr. Zed's mission Medical Mystery, where the Vault Hunter is ordered to test out an E-Tech weapon (seemingly always a BlASSter) belonging to Doc Mercy on the local Bandits. Following this, Zed takes the weapon, but gives a Spiker or Dart as a reward.
The following are the weapon types:
The pistol types are Spiker and Dart. Logan's Gun is a Dart, and the Dahlminator is a Spiker.
These pistols shoot "smart" projectiles that seek out the target you had in crosshairs when shooting. The projectiles are slow-moving, stick to enemies, and explode after a delay; there is no immediate feedback regarding whether a shot has hit, since the damage number only pops up when the round explodes. An important note is that their high damage statistics are offset by the fact that neither type of weapon is able to cause critical hits. Also of note is that these guns will ignore the shield carried by some nomads, so are effective in situations where you must take them head on.
Dart – Hurls projectiles that ricochet of surfaces but stick to enemies.
Hyperion – Boosted accuracy, capacity of ~20 rounds, firing increases accuracy.
Maliwan – Uses Maliwan revolver frame, inherits high damage but low capacity.
Tediore – Standard Tediore reload gimmick.
E-Tech SMGs are called Plasma Casters. They have a special barrel with three muzzles and a flamethrower-like igniter underneath, and fire slow-moving energy balls.
E-Tech shotguns are called Splatguns or Blashters. Projectiles are lobbed.
Splatgun – Launches a single projectile. When it hits a surface, it splits like a MIRV grenade.
Blashter – Launches multiple projectiles.
There is only one assault rifle type and that is the Blaster. The Bandit version of the name is BlASSter.
Dahl – Shoots 3 lasers in a horizontal manner.
Vladof – Ricochets on surfaces.
Bandit – Huge magazine size.
The sniper rifle types are Railer, Hybridification, and Moloko. All E-Tech sniper rifles consume two ammo per shot.
Maliwan – Railer – Always elemental.
Dahl – Railer – Burst fire while zoomed.
Hyperion – Hybridification – Pierces through enemies.
Vladof – Moloko – Ricochets off enemies
Types include PRAZMA CANNON, PBFG, Launcher, and Topneaa. All rocket launchers but PRAZMA CANNON deal maximum damage at a large affected area. It should be noted that they will only deal self damage when they are actually close to you, no matter if you are inside the huge splash range.
PRAZMA CANNON – Hurls balls of energy that leaves and drops more balls of energy as it travels. Only Bandit is able to produce PRAZMA CANNONs.
PBFG – Consumes multiple ammo per shot, causes enemies to take more damage after the shot. Creates a blue sphere around enemies within the blast radius. The acronym may stand for "Pretty Big F***ing Gun". This is most likely a reference to the BFG from the Doom series.
Topneaa – Surrounds enemies in a large radius with damaging energy spheres. Dying enemies encapsulated in a blue sphere of energy will disappear. Consumes only one round per shot.