(devised by The As)
We used to play this in the summer when I was a kid.
The basic idea is to take a set of Monopoly -- preferably at least two sets of Monopoly -- and combine them with other board games where you go around the board repeatedly, such as Squatter, Stockmarket and so on, such that you have four boads. You put them all together (probably on the floor) so that the direction of travel is in a cloverleaf pattern. Thus, instead of going around one board again and again, when you've completed one circuit of one board, you jump to the next board and go around it, and so on, for all four boards.
At one point we had three Monopoly boards: one American, one Australian and one British. The British one had pound signs all over it, so we called it the "Pounds Board". When was on the Pounds Board, the prices of everything doubled, because back then the exchange rate for pounds was 1 - 2 rather than the 1 - 3 it now is.
The real fun was devising our own "action" cards which took account of the "meta" game, such as penalties which made you lose either a Stud Ram or a property, for example.