Doublemove chess is a popular modern chess variant. It was invented by Fred Galvin. Below, you find the rules, and the version now used in AISE, the Italian chess variant organization. Note the (subtle) differences with Marseillais Chess.
The laws of Chess apply, modified as follow:
Originally, the following rules were also used. These rules were abolished by AISE.
Every doublemove must alter the position. A player may not move a piece from a square then back to it, unless the first part of the doublemove was a capture. If a player's first move leaves him no second move save one prohibited by this rules, the games is a draw.
En passant is permitted if when a pawn makes a doublestep and does not advance further, the capture square is vacant, and the opponent captures the pawn on his first move of the next pair.
R. Salvadori - A. Castelli 1-0 (Grand Prix 1995)
1.Nc3// Nc6/e6 2.Nf3/e3 Bb4/b6 3.Ba6/B:c8
(if 3.a3/a:b4?? then N:b4/Qg5!! and Black wins. In fact after the forced 4.Qe2/Kd1, Qf5/N:c2! decides)
3. ... Q:c8/Nf6 4.Ne4/c3 N:e4/Qa6 5.Qe2/Q:a6 Nb8/N:a6 6.Ng5/N:e4 d5/d:e4 7.c:b4/Ke2 N:b4/000 8.Rb1/d4 R:d4/Nc2!! (diagram) and Black wins. If 9.Kf3/Kg3 then N:e3/Rd5!
Hans Kluver, Doppelzugschach. Eine Darlegung des Spiels, Schwalbe, Dezember 1963.