A tougher Trillium: empty columns take Kings only, no exceptions. Two decks, real difficulty, and just a 10% chance of winning it clean.

Lily Solitaire is a tougher version of Trillium, with one added restriction: empty columns can only be filled with a King, not any card. Two decks fill those thirteen tableau piles, and this difficult layout wins only about 10% of the time, mostly on skill.
I'd also recommend Spider Solitaire if you want another challenge. You might also like Trillium Solitaire, the game it builds on.
If you run into anything odd or have an idea that would make the game better, please contact me.
Enjoy the game!
13 tableau piles: Alternate color build down. Cards in sequence down by alternate colors can be moved as a group. Only a King or a group of cards led by a King can fill a space. At the start of the game, each pile is dealt four cards: the 1st and 3rd face-down, the 2nd and 4th face-up.
8 foundation piles: Accept only complete sequences of thirteen cards, Ace to King, built on the tableau; single cards can never be moved to the foundation.
Stock: Clicking the stock deals one card to each tableau pile. There are no redeals.
There are eight foundation piles.
Single cards are never allowed to be moved to the foundation. Only once you've built a complete sequence on the tableau, thirteen cards in order from ace to king, can you transfer it to the foundation.
The top card of each foundation can be moved back into play if another pile will accept it.
Thirteen tableau piles, each dealt four cards at the start. The odd-numbered cards in each pile are dealt face-down, while the even-numbered cards are dealt face-up.
A card can be added to a tableau pile only if it's one rank lower and the opposite color of the pile's current top card, so the only cards that fit on the 5 of spades are the 4 of hearts and the 4 of diamonds.
Cards on the tableau that are not covered by another card can be played onto any other tableau pile.
Only kings may fill empty spots in the tableau.
If the cards are alternately red and black, groups of cards in succession from high to low can be shifted from one tableau column to another.
The stock is made up of leftover cards.
When you click on the stock, a card is dealt to the top of each tableau pile.