Bughouse Chess, Siamese Chess, or Tandem Chess is a variation of chess played with two teams of two people with two chess boards. Team members sit beside each other playing opposite colors. Each player plays his opponent like in a standard chess game except that when pieces are captured they are given to the teammate. The teammate can then decide to place the captured piece almost anywhere on the board in place of a regular move (as in shogi). Team members have to work together, and against a clock, to win. The first board to lose decides the match and if a draw occurs on one board the entire game is a draw.
There are two main variants of Bughouse Chess: Bughouse and Tandem Chess. The main diference is that in Tandem Chess, one cannot use pieces to check or to mate. Also, in Tandem Chess one cannot place pawns on the 1st, 7th or 8th rows if playing white or on the 1st, 2nd, or 8th rows if playing black. In Bughouse anyone can drop any piece anywhere except for pawns on the 1st or 8th row.
Both Bughouse and Tandem Chess use chess clocks to prevent players from waiting indefinitely for a piece (waiting for pieces is considered perfectly acceptable, see bughouse strategy below). Tandem Chess is usually played with 5 minutes per player, and bughouse 3.
Though opinions vary about this, it is generally accepted that at least some form of discussion between teammates is allowed. Any Bughouse variant allows players to ask their partners to capture a specific piece for them.
One of the main ingredients of any bughouse game is time. It is not uncommon for one player to completely stop moving because he knows that any move he makes will result in him getting mated the next move. It is even possible for this to happen on both boards. For example: I am one move away from checkmating my opponent, so he is not moving. However, my teammate is also not moving because any move on his part will result in checkmate. The game now turns into a game of sitting, called a 'Sitzkrieg' (after the German for Sitting War). The game is now decided by whether my teammate or my opponent has the most time left on their clock, because if either runs out of time he will be forced to move and will be immediately loose.
Another very important aspect of Bughouse is player communication. It is customary to announce any big gains or losses ("rook in 3!") and to ask for specific pieces while listing their result ("pawn is rook!"). If you do not do this you might very well find that your partner loses because he was unable to plan ahead for any incoming pieces.
The best place to play is probably on the board (or in this case two boards) with some friends, but in case you don't have enough players a good place to play online is FICS, which is also a good place for normal chess games. To play bughouse you can use clients such as XBoard, Winboard or other clients listed for example on the FICS page.