Pawns may not take a double step on their first move.
Pawns reaching their 8th rank are promoted to any non-Royal piece that was on the board at the start of the game.
Castling is not permitted.
The general rules of turning are modified for these games: instead of automatically turning after moving, the turning is done as a separate move.
For example, imagine a Feeble Alfil at c1, currently turned to the Northeast (this is the position and the orientation in which this piece starts the game). It has three legal moves.
Firstly, it can make an Alfil move to the Northeast, in other words it can leap from c1 to e3, possibly capturing something on the destination square, whether or not the square d2 is occupied.
Second, it can stay where it is and turn 90 degrees to the left, aiming itself at a3.
Third, it can stay in place and turn 90 degrees to the right, which is not a very good idea because the destination square is off the board -- it would have no next move except to turn again.
Instead of moving, it can stay where it is, and flip. If the piece can capture but is not permitted to make a non-capturing move, flipping allows it to move but forbids it to capture; and vice-versa.
You are required to move a piece at least once every 5 moves; you may not simply stay in place and flip or turn. If you have no legal moves at a moment when you are required to move, you have lost by stalemate.
It is illegal to make a move that repeats a previous position, and one can be stalemated by this rule and thereby lose. A position is repeated if all the pieces are in the same place, with the same orientation, and the same capture/move status, and the same player is on the move.
You can win the game by occupying the starting square of the opponent's King with your own King.
If 100 moves have been played without any captures or Pawn advances, the player whose move it is has lost the game.
You cannot win by Bare King; I decided not to use that rule because of the interesting endgame King versus King, which is even a bit difficult with Weakest K versus Weakest K, at least until you get a good feel for it.
There is no flipping.
Pawns have their usual FIDE rules of movement.
Both a Feeble Queen and a Feeble Chancellor are defined, which allows the game to be played with slightly different armies.
The leaping pieces and the powerful Queen or Chancellor make it possible to have slashing attacks with rapid opening development.
The weakness of the King makes the game playable.
The Feeble Queen can turn either 45 degrees or 90 degrees, at will.
Its estimated value is one eighth of a Queen.
The Feeble Chancellor can turn 45 degres, and has the special option of turning only its Knight move or only its short move.
Its estimated value is the same as the Feeble Queen.
The Feeble Alfil turns 90 degrees.
Its estimated value is less than one eighth of a Bishop.
Its estimated value is one eighth of a Knight.
Its estimated value is one twelfth of a Rook.
This is of course the shortest possible game ending in checkmate.
A piece that can move without capturing cannot capture, and vice versa; instead, the piece must first flip (as described above) from one mode to another.
The flipping rule makes the pieces basically half as strong as they are in Feeble Chess.
In addition, the jumping pieces are lame, and the Queen is a Weakest Ferz. With these changes the pieces are as weak as they can be while still retaining some relation to their usual powers.
The weakness of the King makes the game playable.
The Weakest Queen can turn either 90 degrees, or flip.
Its estimated value is less than 1/32 of a Queen.
The Feeble Alfil turns 90 degrees, or flips.
Its estimated value is less than 1/24 of a Bishop.
It cannot leap over an intervening obstacle: for example, it cannot go from b1 to c3 either if b2 is occupied or if c2 is occupied.
Its estimated value is 1/24 of a Knight.
It can turn 90 degrees, or flip.
Its estimated value is 1/24 of a Rook.
Its initial orientation allows it to move but not to capture one square straight forward.
It can flip or it can turn 45 degrees, but of course it can turn to only one of the three forward directions.
This is, I think, the shortest possible game ending in checkmate.
And now to show how the weakness of the enemy pieces can make your pieces strong:
1. e2-e3 e7-e6 2. e4-e4 e6-e5 3. e4 flips; White wins the Pe5 and then has a powerful advantage because anything that approaches e5 can be attacked by turning e5, and so Black's position is cramped.
1. e2-e3 c7-c6 2. e3-e4 c6-c5 3. e4 flips, b7-b6 4. d2-d3 Nb8-c6 5. Ac1-e3 b6 flips 6. Ae3 turns left, b6 turns towards c5 7. Ae3xc5 b6xc5 8. c2-c3 Nc6 flips 9. c3 flips, e7-e6 10. f2 turns to e3, Nc6 turns to e5 11. c3 turns to d4, e6-e5 12. e4xe5 Nc6xe5 13. d3-d4 Ne5 flips 14. d4 flips Ne5 turns to g5 15. d4 turns to c5 c5xd4 16 c3xd4 Ne5-g6
The advantage of the first move is looks powerful, but that is perhaps because I didn't understand the game very well yet when I devised these samples.
1. e2-e3 g7 turns to f6 2. e3-e4 g7-f6 is an example of a better way to start the game.
Its initial orientation allows it to move but not to capture one square straight forward.
It can flip or it can turn 45 degrees, but of course it can turn to only one of the three forward directions.
In order for the Weakest Pawn to change from moving forwards to capturing diagonally, it must flip and it must turn (this takes two moves). Whichever one it does first, it is aimed in a direction it cannot use. This is a little bit ugly, but it certainly is weak.
Weak chess can generally be played in the same amount of time as strong chess, because although there are more moves to be made there is less to think about on each move. The exception is when the time limit is so fast that without an increment there is simply not enough time to physically make the number of moves required to win a game of weak Chess.
Grid Chess is a weak form, and U-Grid Chess even weaker; and many people in the 1970s loved to play them, even by snail mail, when the cost of postage and the number of moves required made it an expensive game to play.
I have played a few hundred games of Shatranj with 7 minutes per side, and greatly enjoyed it; and I loved playtesting Demi Chess.
Feeble Chess and Weakest Chess (which already has two forms) are designed to appeal to those who love weak forms of Chess, and to take to an extreme both the virtues and the vices of such games.
I am proud of both games because as weak as they are they are both recognizably Chess, and I will be very surprised if anybody can devise much weaker games that are still Chesslike.