Knife monopoly is simple, and it makes sense since you are likely to get stabbed in the back in business anyway.

You play regular monopoly, but every time you buy a house you balance a steak knife on the edge of a shelf that is suspended above you. When someone lands on that property, prior to paying you, they get the option to jump up and down on the ground to possibly shake a knife loose. They have to pay double rent for this option. If you get stabbed in the back by a knife, then you lose that property and the houses on that set of properties is cleared from the board. The knives associated with those properties are also removed from the shelf.

If you put a hotel down, then you have to balance a large kitchen knife on the business shelf. If you get stabbed by that knife, you lose a single hotel. If you die from that knife, then you lose 2 hotels.