Gemini is a privately-owned cryptocurrency exchange that allows users to buy, sell, trade, and securely store bitcoin, ether, and about 40 other cryptocurrencies. It was launched in 2015 by Cameron and Tyler Winklevoss.Gemini has a tiered service with separate interfaces and fee structures for casual investors and hardcore traders. It has a mobile app, a payment app, and its own currency, the Gemini dollar. Unlike most cryptocurrencies, the Gemini dollar is a "stable coin" tied to the U.S. dollar.