My NaNoGenMo entry for 2019 is 50,000 words of fictional (and hopefully playable) card games, generated by knitting together fragments of rules from existing games, particularly minor variants and hour rules. The games are bounded into four overlapping groups: trick-taking, climbing, melding and matching. As I found new rules I dropped them into one or more of those groups, each time attempting to spot any obvious contradictions or ambiguities in its interaction with other rules for that group, and to work around it accordingly.
The first edition is at https://kevan.org/nanogenmo/2019firstedition.html
Sample output:
Le Temple
Le Temple (or La Bolle) is a classic French trick-taking game for three to five players where the led suit is weaker than the rest. It uses a standard 52 card pack. Remove 7s and 7s. Cards rank A, K, Q, J, 10, 9, 8, 6, 5, 4, 3, 2.
Setup
Each player is dealt six cards.
Turn the top card of the deck to determine trump suit.
Play
The player to the dealer's left starts by leading any card. If the card led is not a trump, its suit is the small suit for the trick. Players need not follow suit.
The trick is won by the highest trump, or if it contains no trump by the highest card not in the small suit (with the earliest card played breaking ties), or the highest small card if all cards were small. The winner of the trick leads the next trick.
Scoring
When all six tricks have been played each player loses 1 point per heart taken in tricks and loses an additional 9 if they took the 6 of clubs. Taking the 6 of diamonds doubles that player's score for the hand.
When a player's score reaches -40 or lower the player with the highest score wins the game. If tied, the tied player who won a round latest in the game wins.