Mircea Popescu's Options Emporium (MPOE) is an exchange where options (derivative contracts) are traded.
The exchange offers options contracts under the American style where the buyer can execute the option at any time before the option expiry. Options may be executed at any time before the last Friday of the expiration month (up until midnight GMT of the Thursday evening that occurs before the last Friday of that option contract's month).
Though the CALL and PUT options are priced in USDs, all funds for buying and selling options on this exchange occur in bitcoins. Additionally, the funds for executing options occurs only with bitcoins as well. For example, the quote for buying a call option will show a purchase price first computed in dollars but then the payment amount will be a conversion to BTCs based on the market exchange rate at the time of the quotation.
The option contract size is for one bitcoin (1.0 BTC). For example, buying a quantity of 100 CALL @5.0 contracts gives the buyer the option to purchase 100 BTC at $5.00 USD before the option expiry.
All positions are covered -- there are no "naked" short positions. For example, the seller of a 100 CALL @5.0 requires payment of 100 BTC plus the option premium to be sent to the exchange.
Quotations provided are either the best available from existing market positions offered (when size is shown under the "open" column) or are provided by the exchange's own market-making system and are good for order size of up to 1,000 contracts. Requests for quotation of larger sizes are available by contacting the exchange directly (via e-mail).
The exchange is offered and operated by Mircea Popescu of Romania. The site includes a very broad disclaimer of liability as well as the instruction (in red color) to "Read this whole thing first so you don't end up wasting bitcoins".