Sa'Angreal

From the Glossary of the Wheel of Time.

Remnants of the Age of Legends that allow channeling much more of the One Power than would otherwise be possible or safe. A sa'angreal is similar to, but more powerful than, an angreal. The amount of the Power that can be wielded with a sa'angreal compares to the amount that can be handled with an angreal as the Power wielded with the aid of an angreal does to the amount that can be handled unaided. The making of them is no longer known. As with angreal, there are male and female sa'angreal. Only a handful remain, far fewer even than angreal.

Robert Jordan's Wheel of Time:
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Sa'Angreal, the older brother of Angreal, were produced by Aes Sedai and all evidence points to the fact that the creation of these were a great undertaking made by Male and Female Aes Sedai working together in harmony.

Unlike Ter'Angreal and Angreal where there are still hundreds of each in existance, There are very few Sa'Angreal in the world of the Breaking.

Two of these take the form of giant statues half buried the ground, one of a male, one of a female, both holding along spheres aloft. These are the most powerful Sa'Angreal ever created, and were never used because they contain the power to rip the world asunder. These can be activated from a remote location by using a small Ter'Angreal that acts basically like a remote control, not surprisingly, the female statue is for use by a female, and thus draws and holds saidar for her, while the male statue draws and holds saidin.

A third Sa'Angreal is known as Callandor or The Sword That Is Not a Sword, The Sword That Cannont Be Touched. It features prominently in the Prophecies of the Dragon.

As Inoshira_K and Palpz both just pointed out, The White Tower has at least a 'few' Sa`Angreal and Siuan uses one to cure Mat in the Dragon Reborn.