Duke asks a question the rest of the Canfield family never does: does it matter how a reserve is divided? Twelve cards under a single top card give you one choice at a time. The same twelve cards split into four piles of three give you four, every turn, all game. That is the whole design. Four little spreads sit face up beside four single-card columns, an emptied column is never refilled, and the stock turns one card at a time with two redeals. Free in your browser, no sign-up.
Goal: build all four foundations from Ace to King by suit.
Four reserve tops and four columns means eight cards you can act on at any moment, in a game with only 52. That is unusually generous, and the difficulty sits somewhere else: in what you spend those choices on.
Compare Duke with Storehouse, which buries thirteen reserve cards under one playable top. In Storehouse the reserve is a queue: it comes out in one order and you either can use the next card or you cannot. In Duke the reserve is a hand. Twelve cards, four of them live, and you choose which one to spend — so a card that is useless right now can simply be left alone while you work another pile. That is a completely different kind of decision, from an almost identical pile of cards.
It also changes what a bad deal looks like. A Storehouse deal dies when the queue jams. A Duke deal dies when all four tops are dead at once, which is rarer and takes longer to arrive — so Duke plays slower, feels more controllable, and punishes the specific mistake of draining your own options. Players who like FreeCell's open information but want a stock to work with usually take to it quickly.
Because how many cards you can reach matters more than how many cards there are. Twelve cards in one pile give you one playable top; the same twelve split into four piles give you four. Duke exists to make that difference the game, and it is why it plays nothing like Storehouse despite a similar deal.
No, and this is the second thing that sets Duke apart from most of the Canfield family. There is no forced fill at all. An empty column stays empty until you choose to put something in it, and any card may go there, which makes spaces the most valuable thing on the board.
No. Reserves are sources only. A card leaves a reserve for a tableau column or a foundation, and nothing is ever placed onto a reserve from anywhere.
Three times in all: the first pass plus two redeals. Cards are turned one at a time, so you see every card on each pass, which makes the early passes useful for planning even when you cannot play much.
No. Duke uses plain Ace-to-King foundations in suit with no wrap, and the tableau does not wrap either, so a King cannot be packed onto an Ace. That is a difference from Canfield proper, where both do wrap.
Playing from whichever reserve happens to fit, which drains all four piles evenly and leaves you with fewer live tops as the game goes on. Spend from the pile whose next card you actually want, and leave the others alone.