FreeCell
Every card face up, four cells to think with. Almost always winnable.
Cleared.
No legal moves remain — undo a few, or deal a new game.
Build down the columns in alternating colours and send each suit up to its foundation from the Ace. The four cells hold one card each: they are your only spare room, and how many you leave open decides how long a run you can carry — the same goes for empty columns, which are worth twice a cell.
Drag a card, or click it and then click where it should go. Double-click finds the card a home on its own — its foundation if it can, otherwise a build it fits, then a free cell. Keyboard: tab to a card, press Enter to pick it up, tab to a pile, press Enter to drop. Escape cancels. Nothing is dealt face down, so every deal is solvable with enough thought; your game is saved in this browser, so you can close the tab and come back to it.