Communications of the ACM

Since late November, some of the world's savviest cryptocurrency investors have been hooked on a game that has cartoon sheep, cartoon wolves, a digital currency called $wool — and the potential to make real money.

Graham Friedman, a self-described crypto evangelist, is among them. Mr. Friedman put up more than $20,000 of his own money to buy one wolf and one sheep — or, rather, unique digital images of them called nonfungible tokens.

"I'm like, dude, the narrative is so cool," said Mr. Friedman, a director at Republic Crypto, a digital asset strategy company. "I'm here for the waltz."

Wolf Game, as it is called, applies some familiar financial principles to a mysterious digital world. Players can buy sheep from the creator of the game, identified only as "the Shepherd," and lend them back to "the barn" — essentially a storehouse — to earn interest. The payments are in $wool, a digital token that can be used as a form of payment anywhere on the Ethereum blockchain, on which the game is built. To get a sheep back from the barn, players must pay a 20 percent tax in $wool to those who bought digital images of cartoon wolves.