The Eye of Agamotto is a powerful relic created by Agamotto, the first Sorcerer Supreme, to contain the power of the Time Stone inside it. It has been passed down the long line of Sorcerers Supreme that followed him.
The Eye has the ability to manipulate the flow of time and was used by Doctor Strange to fight Kaecilius and Dormammu and restore the Hong Kong Sanctum.
It was placed back in Kamar-Taj until Strange could learn how to control it.
It was destroyed by Thanos during the Battle of Titan, although the Time Stone was no longer inside.