From Wikipedia:
Bughouse chess (also known as Exchange chess, Siamese chess, Tandem chess, Transfer chess, Double bughouse, Cross chess, Swap chess or simply bughouse or bug) is a popular chess variant played on two chessboards by four players in teams of two. Normal chess rules apply, except that captured pieces on one board are passed on to the teammate on the other board, who then has the option of putting these pieces on their board.
The game is usually played at a fast time control; this, together with the passing and dropping of pieces, can make the game look chaotic and random to the casual onlooker; hence the name bughouse, which is slang for mental hospital. The game is traditionally played as a diversion from regular chess both over the board and online. Yearly, several dedicated bughouse tournaments are organised on a national and an international level.
I first learned this fascinating offshoot of chess around 1975. At the time, as far as I knew, the main (or only?) variant was played by just two opponents on a single board, and if you captured a piece you always put it back on the board, on the unoccupied square of your choice.
The "bughouse" concept can be applied to backgammon. I doubt that it would be an interesting game (without further modification), but it is a great concept for the creation of backgammon puzzles.
For backgammon bughouse, let's assume the most straightforward application. All rules are the same as in regular backgammon, except: If you hit one or more checkers, you may (at the end of your turn) place it/them on on the bar OR any point that is not occupied by the opponent. (Multiple checkers do not have to go to the same point.)
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| XGID=-a--a-E-C---dEa--c-e----B-:0:0:1:64:0:0:3:0:10 | |||||
Blue to play 64 | |||||
For example, suppose White opens with 32S as shown above, and Blue rolls 64. If Blue hits with 24/14*, he may put the hit White checker on the bar (the sole option in normal backgammon) OR he can place it on any point that is not occupied by Blue checker(s). [Here, there are twenty options for relocation. This includes the bar, any vacant point, or any point already occupied by White.]
For demonstration purposes, let's say that Blue chooses to place the hit checker on his own 22pt (White's 3pt). We'll notate this play 24/14*=22. Below is the position (with White now on roll) after Blue completes his 24/14*=22 play:
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| XGID=-a--a-E-C---dEA--c-e--a-A-:0:0:-1:00:0:0:3:0:10 | |||||
Blue played 24/14*=22 | |||||
As you can see, "bughouse" rules are simple.
Okay, let's have some fun. Here is a bughouse backgammon puzzle:
Starting from the opening position, find a (bughouse) sequence by which one player obtains a four-point prime and the other player obtains a six-point prime.
Whoever achieves this in the fewest rolls will be the winner. (Multiple submissions are welcome.)
Nack