Merge Congress and Forty and Eight into one eight-pile layout, and you've got Diplomat: medium difficulty, two decks, and a friendly 65% chance of winning.

Diplomat Solitaire is a play on Congress Solitaire and Forty and Eight, two older games that share its eight-pile foundation and tableau layout. Medium difficulty, 65% of hands playable through to the end. Two decks are in play, and getting there takes a blend of skill and luck.
If you like Diplomat, Rows of Four Solitaire is worth a look too, since it's built on the same eight-pile foundation.
If you run into anything odd or have an idea that would make the game better, please contact me.
Enjoy playing!
8 foundation piles: Build up from Ace to King in the same suit. All piles start empty.
8 tableau piles: Build down, regardless of suit. Only the top card of each pile can move, though any card can fill an empty spot. Each pile starts with four cards, dealt face-up.
Stock: Click to deal one card at a time to the waste. There are no redeals.
Waste: The top card can be played on the foundation or tableau.
There are eight foundation piles, all starting empty. An ace can start a new pile.
A card can be added to a foundation pile only if it's one rank higher and the same suit as the pile's current top card, so the only card that fits on a Queen of hearts is the King of hearts. Each pile holds up to 13 cards.
The top card of each foundation can be moved back into play if another pile will accept it.
There are eight tableau piles of four cards each, all dealt face-up.
A card can be added to a tableau pile only if it's one rank lower than the pile's current top card, regardless of suit, so the only card that fits on a five is a four of any suit.
Any tableau card that isn't covered by another card can be played onto the foundation or any non-empty tableau pile.
Any card can fill an empty tableau spot, whether it comes from the waste pile, the foundation, or another tableau pile.
Only one card may be moved at a time; sequences are not permitted.
There's one waste pile, and the remaining 72 cards make up the stock.
Click the stock to deal one card to the waste. You get only one pass through the stock.
The top waste card can be played to the tableau or foundation.