Keys "s"=save "l"=load "b"=back once
Mark Liptak and Rick Babcock, 1990. The object is to checkmate the other side's primary (white/black) king. You move whatever friendly units are on your own board during your turn. Neither secondary player may expose either of the side's kings to check. If the primary player exposes the secondary king to check, the secondary player is paralyzed and primary player takes the turn instead. If secondary king is temporarily mated, pieces are frozen and uncapturable. Unfreeze by moving primary king to the other board.
These are simple illustrations rather than strong opponents.
Bug reports? -- Thank you! Keep them coming!