The Diablo III website previews Kanai's Cube, one of the new features in the upcoming version 2.3.0 patch for the action/RPG sequel which they say is "set to change the foundation of Diablo III as we know it." They also note that this item is a tribute to Kevin Kanai Griffith, a Blizzard artist and Diablo fan who died of cancer last year. The item has several functions, including the ability to reforge legendary items and to provide a use for legendary items you can't trash because they have intriguing powers but can't actually use, as they explain here:

One of the first, most frequent powers you’ll utilize is the ability to extract a Legendary power from an item. This will add the power to your collection list, a comprehensive history detailing the vast amount of powers you’ve amassed. This also allows your hero to equip a Legendary power without having the item equipped, clearing up your stash of all those items you’ve been keeping “just in case.” You’ll be able to equip one power each from three categories:

• Weapons
  • Includes all main hand and off-hand items, including Shields, Mojos, Quivers, and the like
• Armor
  • Virtually everything else; Hands, Legs, Feet, Chest, Belt, Wrists, Shoulders, and Head
• Jewelry
  • Rings and Amulets

Characters may only equip powers from items that their class can normally equip. Powers are also extracted at their most potent value, making it a tough decision between equipping a well-rolled item or melting it down to utilize a maximized power. Powers can be extracted from any level Legendary. Finally, don’t worry if you get tired of a particular ability—you’ll be able to swap freely between the powers you’ve collected at any time by visiting Kanai’s Cube.