The Infinity Weapons are weapons created by Galath, the Worker of Secrets. They are all able to disrupt the Quantum Identity Pattern of a Deathless. In Infinity Blade III, the Worker of Secrets gives all of his Infinity Weapons (except for the modern Infinity Blade and Infinity Edge, which are sold in store) to major Deathless who follow him. They all have a similar black-and-silver color scheme, except the original Infinity Blade. Owning all the infinity weapons and bringing them back to the Seccian Dessert will give you the light weapon "Infinity Blade" for Isa and Siris.
All the Infinity Weapons
The Infinity Blade[]
The Infinity Blade is the main catalyst of the Infinity Blade trilogy. It is the first Infinity Weapon created by Galath, the Worker of Secrets, to undo his invention of the Deathless. When used against one, it destabilizes the opponent's QIP, therefore granting him or her a "true death".
The Infinity Blade (Modern)[]
The new Infinity Blade is a copy of the original Infinity Blade made by Galath, the Worker of Secrets, to make certain that it could be replicated successfully. It was also meant to serve the purpose of distracting the resistance against the Worker. The Infinity Blade is a light Infinity Weapon in Infinity Blade III, able to be bought in the store for 
600,000. It is used by Siris.
The Infinity Cleaver
The Infinity Cleaver is a locked, heavy infinity weapon, and also the first Infinity Weapon revealed. It is obtained by defeating the Soulless Raidriar (the God King) in Act I, and is used by Siris.
The Infinity Swords
The Infinity Swords are locked, dual Infinity Weapons. It was included in the first content pack update, Soul Hunter. It is obtained by defeating Oslim (the Deathless Bloodmage) in the Interlude, and is used by Siris.
The Infinity Edge
The Infinity Edge is a light Infinity Weapon, able to be bought in the store for 600,000. It was included in the second content pack update, Ausar Rising, and is used by Isa.
The Infinity Spear
The Infinity Spear is a locked, heavy Infinity Weapon. It is obtained by defeating Therin (the Killer of Dreams) in Act III, and is used by Isa.
The Infinity Daggers
The Infinity Daggers are locked, dual Infinity Weapons. It is obtained by battling Lelindre (Mistress of the End) in Act IV, and is used by Isa.