From Tar Valon Library
Sa'angreal are objects like angreal that allow a person to channel more of the One Power than they could unaided, but are much stronger, and rarer than angreal. A sa’angreal “can be said to allow one to channel as much more of the One Power over that of the angreal as the angreal does over channeling unaided.” The making of them has been lost since the Age of Legends, but some still exist, having been found again since the chaos of the Breaking. They are specific to men or women, though rumors exist of ones that can be used by either. It is not known if there is a continuous gradation between angreal and sa'angreal, or if there is a discrete difference.
- The Choedan Kal
Two giant sa'angreal, created during the War of the Power to be used against the Shadow. They were not used at that time, as the ter'angreal required to access them were lost, but were since used to cleanse the taint. They are the most powerful made.
A flawed sa'angreal in the form of a crystal sword, connected to the Dragon Reborn by prophecy. A man alone can not use it as it lacks the protection against drawing too much of the Power and can also magnify the taint madness. After the Choedna Kal, this is the strongest known to the Aes Sedai (TDR, Ch. 29), but according to Lanfear, there is one other stronger sa'angreal that a man can use (TSR, Ch. 9)
Only two more powerful were ever made, and thank the Light, neither of those was ever used. With Callandor in your hands, child, you could level a city at one blow (Siuan to Nynaeve, The Dragon Reborn, Chapter 29).
“There are only two more powerful that a man can use. One at least, I know, still exists" (Lanfear, The Shadow Rising, Chapter 9)