p.boxed
  | The board is initially empty.
  | Add a piece (not giving check) or move one at each turn.

p.
  The king can be added at any moment, but while he hasn't landed
  no capture can be done. So you could move or land your king "into check"
  if your opponent didn't land his king yet.

p.
  Giving check with a landed piece is forbidden
  (assuming both kings are on the board).

p.
  Pawns can be landed on the four first ranks only. A pawn on the first
  rank can jump two squares, and be captured en passant.

figure.diagram-container
  .diagram.diag12
    | fen:8/8/3b2r1/3R4/k3Q3/3R4/8/8:
  .diagram.diag22
    | fen:8/8/K2b2r1/3R4/k1N1Q3/3R4/5q2/8:
  figcaption.
    Left: no white king, so the black king is safe.
    Right: black to move, there is no way to avoid mate.

h3 Source

p
  a(href="https://www.chessvariants.com/diffsetup.dir/unachess.html")
    | Unachess II
  |  on chessvariants.com. Unachess I gives a too large advantage
  | to white, in the few games I could play.

p Inventors: Jeff Miller and Edward Jackman (1995)