OpenPref is an implementation of European trick-taking game Preferans against two virtual players. It allows to play Sochi version of Preferans, allowing to change some game conventions.
Preferans is played by three active players with a French-suited 32-card piquet deck. Aces rank high and tens rank in their natural position between jacks and nines. As happens with many three-player trick-taking games, the game is frequently played by four players using the convention that in each hand the dealer pauses. Each active player receives 10 cards in batches of 2. The remaining 2 cards form a talon that will be used by the declarer to improve his or her hand. The deal typically follows the scheme: 2–talon–2–2–2–2....
Also two players can play Preferans. This variation is called hussar (Russian: Gusarik). In this variation cards are dealt for three players. The third player is called dummy, his cards are not opened during bidding. If someone wins a bidding and the second player decides to whist, his and dummy's hands will be displayed face-up on the table and the defender will play in the light as in the game with three or four players.
A bidding process is used to decide which player declares the trump suit, as well as the contract, which is the required number of tricks the soloist must attain. The soloist is known as the declarer, and the declarer's objective is to win the contracted number of tricks, while the defenders' main objective is to prevent this.
Trick-play differs from Whist in that there is an obligation to trump. The eldest hand leads to the first trick. Players must follow suit if possible, else trump if possible. The trick is won by the player who played the highest trump or the highest card of the suit led. The winner of a trick leads to the next trick.