The Cornerstone of the World is a feature added in Diablo: Hellfire, which allows players to transfer items from one character to another. It is always located in a square room on the first level of the Demon Crypts. When dropping an item on this stone, the character will hear a story about the building of a great cathedral near Tristram, which had a cornerstone made of the rare stone Antyrael. If you return to the cornerstone of the world with another character, the dropped item will be there, provided the character who dropped it was not saved on the same level.
Due to a bug, the item dropped on the stone will sometimes be duplicated and will still appear to the character who dropped it. Due to another bug, a pile of "0 gold pieces" will sometimes spawn on the cornerstone - if this happens, simply pick up this pile to make it disappear.