Sjaak is a general chess-like engine which plays a number of variants in addition to normal chess. The list of variants supported by this release includes:
- Normal chess
- Spartan chess, where black and white play with different armies and black has two kings.
- The Maharaja and the Sepoys*, where white has only one piece (the Maharaja).
- Amazon chess*, where the queen moves as an amazon.
- Knightmate, where the king moves as a knight and the knights move as a king.
- Shatranj, a historic precursor of modern chess.
- Capablanca Chess, a variant played on a 10x8 board with two extra pieces.
- Gothic Chess, the same as Capablanca Chess but with a different starting position.
- Makruk, the Thai version of Chess.
- Courier chess, a medieval variant played on a 12x8 board.
- Chinese chess (Xiangqi), Black and white face eachother across the river that runs along the board, with their kings confined to their palaces.
Xiangqi support is new and hasn't been extensively tested, but seems to work correctly from looking at a number of trial games. The evaluation is probably completely off, so the program will probably play quite badly.
There's one other new feature in this version, which is support for running a match at fixed node-count. To make this work in XBoard, specify the desired NPS and set a fixed search depth of 1. The more general method of specifying pseudo-seconds for the time control does not work and any attempt to select a particular NPS at some other time control will likely not work as intended (it will pop up a warning).
The code has been cleaned up and optimised in many places and some new evaluation terms have been added. In terms of strength, this version should do much better than the previous release in nearly all variants. I'm seeing a small regression in Spartan Chess in my local tests, which I'm hoping to address in the near future, but there's enough new stuff that a new release seems justified. I'm hoping to improve it a bit more for the upcoming 10x8 tournament.
One final note: the pre-compiled downloads contain 32 and 64 bit binaries for Windows and Linux and a universal 32/64 bit binary for OS X. The Windows and Linux downloads further have an SSE4 and an SSE3 version for older hardware. Please let me know if there are issues with these.