Bitcoin isn't the only cryptocurrency on a hot streak—plenty of alternative currencies have enjoyed rallies alongside the Epic Bitcoin Bull Run of 2017. One of the most intriguing examples is also among the most obscure in the cryptocurrency world. Called IOTA, it has jumped in total value from just over $4 billion to more than $10 billion in a little over two weeks. But that isn't what makes it interesting. What makes it interesting is that it isn't based on a blockchain at all; it's something else entirely.

[...] Instead of a blockchain, IOTA uses a "tangle," which is based on a mathematical concept called a directed acyclic graph. Sønstebø says his team pursued an alternative approach after deciding that blockchains are too costly—it has recently cost as much as $20 per Bitcoin transaction because of high demand—and inefficient to operate at the scale required for the Internet of things.

[...] So IOTA has dispensed with the miners. Instead, when a user issues a transaction, that individual also validates two randomly selected previous transactions, each of which refer to two other previous transactions, and so on. As new transactions mount, a "tangled web of confirmation" grows, says Sønstebø.