p.boxed
  | Pieces in the first half of the board are yours. Captures are mandatory.

p.
  All pieces are of the same color (black on the website), but in fact
  pieces just have no color: you control all
  pieces which stand in the half-board in front of you. These pieces can
  only capture on the other half-board.

p.
  Since captures are mandatory, pieces could make some round-trips
  around the board, changing owner at every mid-board crossing.
  For example on the following diagram, the sequence will be 1.Rxd7 Rxd1
  2.Rxd8 and black would win, assuming the final rank is 8th.

figure.diagram-container
  .diagram.diag12
    | fen:3b4/3k4/8/8/8/8/3r4/3n4:
  .diagram.diag22
    | fen:3b4/3r4/8/8/8/8/8/3n4:
  figcaption Before and after Rxd7

p.
  Kings have no royal status, and move like orthodox queens.
  Knights become knightriders: they can make any number of knight steps in a
  direction. There are no en-passant captures, and no castle.

h3 Source

p
  | Strongly inspired by 
  a(href="http://www.wunderland.com/WTS/Andy/Games/monochess.html")
    | Monochrome Chess
  | , but I wanted a version without points counting.

p Inventor: Andrew Looney (1996)