Forty Thieves — Unlimited
Forty cards in ten columns, two full decks, and a rule book with no mercy: one card at a time, same-suit builds, one trip through the stock.
How to play
Eight foundations climb ace to king by suit — all one hundred and four cards belong there. On the tableau, build down in suit, moving a single card at a time; any card may claim an empty column, and empty columns are the only leverage you get. The stock deals one card per tap and never recycles, so every draw is a commitment. This is the classic expert's solitaire: raw win rates run low, but unlimited undo turns it into a puzzle you can actually study.
Questions people ask
Why is Forty Thieves so hard?
Single-card moves and a one-pass stock leave no slack — a buried card stays buried unless you engineer an empty column. Wins are earned, not dealt.
Why are there eight foundations?
Two full decks are in play, so each suit builds twice. Either matching foundation accepts a card.
Any opening advice?
Empty a short column early, even at cost — it's the only place to stage cards — and don't deal from the stock while any tableau move improves your position.