Question: After suing Mark Zuckerberg, who started a digital currency exchange?

Context paragraphs:
Buttercoin: Buttercoin was a private American start-up company that provided digital currency exchange services to the US.  Specifically, Buttercoin operated a full order book trading platform for buying and selling bitcoins.

Gold Age: The Gold Age was a digital currency exchange and one of the first independent e-gold exchanges.  Gold Age was a registered legal corporate entity of Panama.  The Gold Age was launched in 1999 and closed down by regulators in 2006.

Bitcoin Group: Bitcoin Group is a multinational bitcoin mining company headquartered in Melbourne, Australia.  The company was founded during 2014 as a result of a partnership between Sam Lee, Allan Guo and Ryan Xu.  The company announced that it would pursue an initial public offering (IPO) on the Australian Securities Exchange (ASX) in October 2014, however it was delayed due to two stop orders from the Australian Securities and Investments Commission (ASIC).  Bitcoin Group is currently in the process of making a third attempt to list on the ASX through an IPO, it is expected to occur in January 2016 due to ASIC's request for an Independent Expert Report.  The company maintains it is the first digital currency company in the world to IPO as it has avoided going through so-called 'backdoor listings' that have been undertaken by other listed digital currency companies.

Gemini (digital currency exchange): Gemini is a digital currency exchanger started by the Winklevoss twins in 2015.

Uncovered interest arbitrage: Uncovered interest arbitrage is an arbitrage trading strategy whereby an investor capitalizes on the interest rate differential between two countries.  Unlike covered interest arbitrage, uncovered interest arbitrage involves no hedging of foreign exchange risk with the use of forward contracts or any other contract.  The strategy involves risk, as an investor exposed to exchange rate fluctuations is speculating that exchange rates will remain favorable enough for arbitrage to be profitable.  The opportunity to earn profits arises from the reality that the uncovered interest rate parity condition does not constantly hold—that is, the interest rate on investments in one country's currency does not always equal the interest rate on foreign-currency investments plus the rate of appreciation that is expected for the foreign currency relative to the domestic currency.  When a discrepancy between these occurs, investors who are willing to take on risk will not be indifferent between the two possible locations of investment, and will invest in whichever currency is expected to offer a higher rate of return including currency exchange gains or losses (perhaps adjusted for a risk premium).

National Center for Foreign Commerce: The National Center for Foreign Commerce, (Spanish: "Centro Nacional de Comercio Exterior" , CENCOEX), formerly the Commission for the Administration of Currency Exchange (Comisión de Administración de Divisas CADIVI), is the Venezuelan government body which administers legal currency exchange in Venezuela.  The official buy/sell exchange rate was initially fixed at Bs.F.  4.28 / Bs.F.  4.30 per US Dollar (USD).  Currently the official buy/sell exchange rate is fixed at Bs.F.  10 per USD.

Foreign exchange company: A non-bank foreign exchange company also known as foreign exchange broker or simply forex broker is a company that offers currency exchange and international payments to private individuals and companies.  The term is typically used for currency exchange companies that offer physical delivery rather than speculative trading.  i.e., there is a physical delivery of currency to a bank account.

Winklevoss twins: The Winklevoss twins (born August 21, 1981; also humorously referred to as the Winklevi or Winklevii) are American rowers and Internet entrepreneurs, Cameron Winklevoss and Tyler Winklevoss.  They competed in the men's pair rowing event at the 2008 Beijing Olympics.  They are known for co-founding HarvardConnection (later renamed ConnectU) along with Harvard University classmate Divya Narendra.  In 2004, the Winklevoss brothers sued Facebook founder Mark Zuckerberg, claiming he stole their ConnectU idea to create the popular social networking site, and ultimately received $65 million.

Counterparty (technology): Counterparty is a financial platform for creating peer-to-peer financial applications on the bitcoin blockchain.  The protocol specification and all Counterparty software is open source.  The reference client is counterpartyd and a web wallet called Counterwallet showcases all protocol features.  The protocol’s native currency, XCP, is the fuel that powers Counterparty.  It is slightly deflationary, with approximately 2.6 million XCP having been created by burning Bitcoins in January 2014.  Counterparty provides users with the world's first functioning decentralized digital currency exchange, as well as the ability to create their own virtual assets, issue dividends, create price feeds, bets and contracts for difference.

Currency Exchange International: Currency Exchange International (CXI) is a foreign currency exchange company in the United States.

Supporting paragraphs: Gemini (digital currency exchange) Winklevoss twins
Answer: The Winklevoss twins