"You have quite a treasure there in that Horadric Handbag!" A friend dressed as Deckard Cain for Halloween one year. "You have quite a treasure there in that Horadric Cup!" he'd declare, identifying everyone's possessions. "You have quite a treasure there in that Horadric Hat!"
If Diablo II's Horadric Cube could bring such joy, what about an even more powerful cube? Blizzard will introduce Kanai's Cube to Diablo III [official site] in the next big update, with powers like turning a Legendary item's special effects into a passive skill. You'll find it in a new zone.
"Those who played Diablo II might remember the Horadric Cube, a unique device which allowed you to combine items. Useful as it was, it was easily surpassed in power by the item from which it originated, Kanai's Cube. In Patch 2.3.0, players will be able to discover this powerful ancient relic and utilize its incredible potential, including the ability to break down Legendary items and equip their special effects as passive skills (which are separate from your other passive skills), convert crafting materials from one type to another, and so much more."
Ooh! Sounds useful, that. Though if you can't also use it as a secondary inventory and make your pals wait around in the Durance of Hate as you shuffle items in and out, I don't care.
You'll find the Cube in the Ruins of Sescheron, a new zone with new enemies. Patch 2.3.0 will also rework crafting a little, add new Torment difficulty levels, bosh in new Legendary and set items, and more. Check the test realm notes for the skinny.