What unusual engines do we have?

Question

Almost all current engines are similar and built for the same tasks (stockfish, lc0, slowchess, comodo...). And I only heard about a few unusual engines

Crystal: based on Stockfish but used for problem solving

SimpleEval: as I know also built on Stockfish, uses only material counting (1, 3, 3, 5, 9) as evaluation

Boris-Trapsky: plays not the strongest position, but position in which a person is likely to make a mistake

Maia: try to play like human

There are also different game modes in Komodo, but they are not free.

From serious and large projects, I heard only about this. I would like to know if there are similar engines, it is not necessary that the engine plays very well or was created by a large company, the main thing is that it is not ordinary.

Answer 1

Dr Tom Murphy examines 30 interesting chess algorithms in a joke paper for SIGBOVIK 2019, which can be read here:

http://tom7.org/chess/weak.pdf

Among them are strategies such as:

• "worstfish", which plays the worst move according to Stockfish
• Various neural networks strategies, some of which are given modified views of the board
• A strategy that plays the move that minimises the number of resulting legal moves for the opponent
• "equalizer", which prefers to move pieces that have been moved the fewest times
• Less popular classical chess engines such as Topple and ChessMaster for the NES

A video version of the paper is also available: https://www.youtube.com/watch?v=DpXy041BIlA

Answer 2

One that is different is CorChess. CorChess was designed having correspondence chess in mind. Later it has been adapted to be competitive in any kind of time control. It is 100% free. Here is the link: https://chess.massimilianogoi.com/download/corchess/

Lichess uses Stockfish, but something interesting is that level 1 makes mistakes on purpose. So, it is like a Stockfish reversed! People who just learned the rules of chess can defeat it! In the following link, you need to select play against the computer, and then select level 1: https://lichess.org/

About your comment that all engines are equal... I am not an expert, but as far as I know Stockfish tries to search and calculate all the possibilities but Leela Chess Zero (LC0) uses a different system, using probabilities and neural networks.

If you love to learn more about chess engines, my favorite website is https://chessengines.blogspot.com/

They also have a weekly free magazine that I highly recommend to you.

P.S. Even though the last version of Komodo is not free, they have been sharing previous versions for free. At this time, the latest version that is free is Komodo 13. You can download it here: https://komodochess.com/

Answer 3

Leela Zero with one node is an interesting engine setting in Sadler's book The Silicon Road to Chess Improvement, as it doesn't do any search but relies purely on its neural net evaluation function. This makes it "plays like a positional genius with flawed tactics". See more here: How to play with Leela Zero restricted to a one-node search?

ShashChess is unusual in its evaluation as "The goal is to apply Alexander Shashin theory exposed on the following book: Best Play: A New Method For Discovering The Strongest Move by Alexander Sashin."

ice4 is a chess engine in only 4096 bytes! It implements many standard engine features like Zobrist hashing, transposition tables, PV search with quiescence and null move pruning, iterative deepening, and more.