Madrasi Chess is a fairy variant of chess where units (King excepted) are paralyzed when attacked by an enemy unit of the same nature. A paralyzed unit cannot move and does not give check ("Checks are fairy"). It can only paralyze enemy pieces, including its own paralyzer.
Here is a simple example:
2711 - N. Plaksin
3rd Hon. Mention, diagrammes 1991-92
8+8. Is this possible? (Madrasi)
The genre was invented in 1979 (that is, quite recently) by A. J. Karwathar. It immediately became very succesful because it allowed many very nice effects. In my opinion, this is due to the original restriction that only a B can paralyze another B, a Q another Q, etc. Therefore a given piece does not only attack/defend according to the moves it can perform, but also according to the positions of enemy men of the same nature.
One detail: en-passant capture is possible because the P which made a double step does not paralyze the enemy P on the 5th rank. The pawn which made a double step is paralysed for half a move though (so it doesn't give check!) Ivan Skoba wrote an article on en passant in Pat a Mat 29, a summary of the article can be found at Chess Composition Microweb
Isardam (or Madrasi reverted) is a fairy genre where only moves that do not lead to a Madrasi paralysis are legal. The restriction also applies to the King capture after "check" so that a move does not give check if capturing the K would lead to a Madrasi paralysis. Again, "checks are fairy".