Antichess
Lose all your pieces (or get stalemated) to win the game.
Also known as Losing Chess or Giveaway. The aim is upside down: get rid of all
your pieces.
The rules
You win by having no pieces left, or by having no legal move — being stalemated
is a win here, not a draw.
Capturing is compulsory. If you can take something, you must. When several
captures are available you may choose between them, and that choice is usually
the whole game.
The king is an ordinary piece. There is no check, no checkmate, and no castling;
the king can be captured like anything else, and a pawn may promote to a king.
What changes
Material is a burden, not an asset. Winning a queen is normally a disaster.
Because captures are forced, a single move can set off a long chain in which
neither side has any choice. Play consists largely of arranging those chains so
that they end well for you.
What to watch for
Read the forcing line to the end before you enter it. In ordinary chess a
miscalculation costs a pawn. Here it usually costs the game, because you cannot
stop halfway.
Avoid giving your opponent a choice of captures. Leaving exactly one capture
available is how you steer them; leaving two hands the game back.
White is generally thought to have a strong advantage with best play — 1.e3 in
particular is a known problem for Black.