Twelve columns dealt four deep, plus a fifteen-card reserve to bail you out when three jammed decks fill the tableau fast.

Minerva Solitaire scaled up to three decks by Thomas Warfield: twelve foundation piles, twelve tableau columns dealt four cards deep, and one wide reserve of fifteen cards to draw from. With three decks, cards jam up fast, so the reserve's extra room matters even more than in the original.
Triple Minerva fans who want a breather should try the classic Solitaire, no reserve pile required.
If you run into anything odd or have an idea that would make the game better, please contact me.
Enjoy yourself!
12 foundation piles: Build up from Ace to King in the same suit.
12 tableau piles: Build down by alternating color, and move alternating-color sequences as a group. Four cards are dealt to each pile, with the odd-numbered cards face down. Empty columns can only be filled by a King, or a valid King-led run.
Reserve: Fifteen cards are dealt here face-up at the start. Only the top card is available, and it may be played to the tableau or the foundations.
Stock: Click to flip cards one at a time to the waste. You get two passes through the stock in total.
Waste: The top card is playable.
There are twelve foundation piles.
An ace already on the foundation can move to any vacant foundation pile.
A card can be added to a foundation pile if it's one rank higher than the pile's top card and the same suit. So the only card that fits on an 8 of spades is a 9 of spades. Each pile holds at most 13 cards.
The top card of each foundation can move back into play if another pile will accept it.
The reserve starts with fifteen cards, all dealt face-up. No card may be moved into it. The top card can be played to the tableau or a foundation.
Each of the twelve tableau piles gets four cards, odd-numbered face down and even-numbered face up.
A card can be added to a tableau pile if it's one rank lower than the pile's top card and the opposite color. So a J of spades or J of clubs can be played on a Q of diamonds.
Any uncovered tableau card is free to move to the foundation or another tableau pile.
A King, or a valid King-led run, is the only thing that may fill an empty tableau column.
An alternating-color sequence, high to low, can move from one tableau pile to another as a group.
There's one waste pile; everything else makes up the stock.
Click the stock to deal one card to the waste. You get two passes through the stock before it's exhausted.
The top card of the waste can be played to the tableau or foundation.