Don’t know what it is, but I love it!

Many many years ago I became aware of a game in which each player receives an envelope containing various denominations of play money and a few slips of paper with rules on them: "X blue bills are worth X^2 in total", "Each yellow bill is worth 10 ONLY if its envelope has zero green bills", "Each pink bill is worth the number of different colors in its envelope", etc. Players may freely trade information or bills, and at the end of a time limit must submit an envelope for scoring, which is subject to ALL scoring rules that have been distributed.