Since the 666 Satan tier list is well underway, I think I'll go ahead and start a O-Part tier list as well, using the canon O-Part ranking system. In case you don't know what O-Parts are, or what the ranking is like; O-Parts are mysterious tools and created from the technology of an invading alien species, that only function when wielded by descendents of said aliens, known as O-Part Tacticians (or OPT for short) via kind of a life energy known as Spirit.
As for the ranking system, it was created by the Stea Government as a way to measure the power and usefulness of an O-Part. The system ranks O-Parts from E rank, all the way up to SS rank. This is the same system I'll be using to tier the O-Parts, and I'm copying almost every description directly from the O-Part catalogue found in most volumes of the manga.
Note: Most of the ones listed now are post-timeskip, I'll add more Pre-timeskip O-Parts tomorrow, and I'll probably add the O-Part type and OPT eventually as well.
O-Part: Shin Effect: Zol, allows Sealed Shin to rip out nearby souls, with an AoE of at least several miles. Can also utilize barriers, and create immense beams of energy. True Shin has all of the abilities of the Angels and Demons of the Formal Kabbalah and Reverse Kabbalah, as well as dozens, possibly hundreds of other abilities from pretty much every O-Part ever shown.
O-Part: Heavy Metal Effect: Metal guard, weight control. This is basically a full body armor version of the Giant's Knife that Kite used previously.
O-Part: Franken Schretz Effect: Mask connection (integration), ultrasonic blade, fire and ice mask. Created by his father Browny, this OPT has a body made up of various O-Parts. Browny built it in the image of Franken's favorite mask.
O-Part: Twelve Watchers Effect: Black laser, handling. Each piece can shoot a black, high-energy laser. Putting parts into fixed shapes can intensify the laser.
O-Part: Fairing Effect: Sound materialization. Has the ability to materialize the letters of almost any word or sound that goes through it.
O-Part: Red Spear Effect: To compress and control light. It enables the wielder to manipulate light within its given range. Using this O-Part is like holding the sun in your hands.
O-Part: New Big Orphan Effect: A large vehicle that can fly in all directions.
O-Part: New Zero-Shiki R Effect: Creates it's blades in relation to an opponent's level of hatred.
O-Part: Tricky Effect: Magnetism. Smaller then Ball's old O-Part, but stronger and trickier.
O-Part: Garaia Effect: Flight, rust beat. Turns anything it bites into rust.
O-Part: Right Hand and Left Hand Effect: Super tight grip. Can squeeze all the blood out of a person.
O-Part: Staring Mirror Effect: Materialization of the inner psyche, a stone mirror made from gil ore. It has the power to reflect even the deepest areas of any persons inner psyche, no matter how powerful that person may be.
O-Part: New Big Orphan Angel Effect: Flight, healing. Improved Big Orphan, with the ability to heal those inside it.
O-Part: Tithonium Body Effect: The densest metal in the world, can also project lasers.
O-Part: Rainbow (hand tattoo) Effect: Favorite trick is gravity control. The seven tattoos each have a different power, and so the name: Seven Colors Amidaba. Her favorite trick is gravity control.
O-Part: Tithonium Gun Effect: Browny Schretz used tithonium, the hardest metal in the world, to create his right arm. It looks like an ordinary arm, but is actually a power compressor that shoots highly compresses gas. It's one of the only weapons that can break Tithonium itself.
O-Part: ? Effect: Thunder. An axe weapon that can generate electricity. More powerful then Jin's Ashura.
O-Part: Ashura Effect: Flame. Initially, due to Jin's hatred, it's effect became black flames that cannot be put out until it's finished burning it's target.
O-Part: Zero (remodeled) Effect: Triples energy, wind attack. Jio's boomerang after being modified by Kirin, more powerful and durable then the old Zero. Jio can also use it to create a tornado-like blast of wind.