Crushed Chess

The original author of this variant is unknown to us, and perhaps it has been invented more than once. An email from Scott de Brestian to Sam Trenholme gives it as "King of the Mountain," but the transcript here (about halfway through) doesn't list the date; another email there is dated 1993. Clifford Pickover gives the game as "Crushed Chess" as section 56.11 of his 1992 Mazes for the Mind. Pritchard's Classified Encyclopedia includes the game in section 3.5, citing Pickover.

Rules

As usual, except that after every 10 turns (each player gets 10 moves), the outermost squares disappear along with any pieces on them. Win by having your king survive longer—either capture the enemy king or have it lost to the edge (the game is a draw if both kings disappear at the same time).

Notes

Some details of the rules may differ by source.

The mail from Scott de Brestian suggests that checkmate wins (possibly saving a loss/draw by losing one's own king before the next turn, or losing one of the checkmating pieces). Pritchard, following Pickover, gives a win only by a longer-surviving king.