Full Deck: Euchre, Spades, Hearts, and More

Eight games. One deck
Most card games on Steam are one game. This is the whole shelf: the Euchre family and the classics that share its bones, all dealt from the same deck, with the same rules for following suit, taking tricks, and counting up afterwards.

Euchre— 24 cards, four players, two teams. Order it up, go alone, get euchred.
Token Bid Euchre — bid with tokens you earn to power up bad hands. Go into debt and it follows you.
Anti-Euchre — the contract runs backwards. Every trick you take is a trick against you.
Double Trouble— one hand, two segments, bid separately and scored together. (Two things called per hand)
Triple Threat — three segments and 210 legal declarations. There is no safe bid. (Three things called per hand)
Spades — nil, blind nil, and the bags that come back for you ten hands later.
Hearts — duck every point, or take all of them and hand them to everybody else.
Oh Hell — bid your tricks exactly. One over or under and the hand is worth nothing.

You don't have to already know how to play
Every one of the eight has a guided tutorial that deals a real hand and plays it with you. The table stops and waits while you read. It points at the card it is talking about. And if you are about to make the mistake it just warned you about, it doesn't let you — it tells you why instead.
That matters most for the four Euchre variants, which you will not find anywhere else and cannot look up.
Opponents that are actually playing
Four difficulty tiers, and what separates them is what they are allowed to know — not how much they cheat.

Easy forgets what has already been played.
]Medium remembers trump, and who is out of what.
Hard counts the entire deck.
The fourth tier is a rare "mini boss" level challenge. Beating it is not meant to be routine and is a real achievement.

Your table, your rules
Every family plays it differently, and this one doesn't argue with you. Sixty house rules across the eight games — stick the dealer, screw the dealer, no-trump, bag penalties, scoring floors, what the Jack does, what happens on a misdeal. Change them, save the result as a preset, and play it.
Changing the rules doesn't lock anything off. Custom rulesets still earn achievements.