HAGGLE is a thinking game for a large group of people. It can be played at a party or over the course of a full day.
One person serves as moderator, and devises a secret set of scoring rules and prepares a number of colored cards for use as scoring markers. The moderator starts the game by handing each player a sealed envelope containing a small number of colored cards and a couple of scoring rules such as "Orange cards are worth twice the value of blue cards" and "Each white card is worth 5 points unless the player turns in any black cards, in which case white cards are worthless." Players may trade cards and/or information in an attempt to acquire the most valuable hand of cards, all or some of which must be turned in to the moderator at a specified time. When the deadline passes, the moderator scores each player's cards based on all the scoring rules, and the highest score wins.
A write-up of the original game as it appeared in Sackson's "A Gamut of Games", back in 1969. It includes a quick explanation of Haggle, and the "rule cards".
In this version of Haggle, players have discovered the remains of a spell book torn from its bindings along with some spell ingredients. Their goal is to create the most potent spell through negotiation and trade.