user33414: 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.

user10075: 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

user17004: 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/

33414: <p>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</p>
<p>Crystal: based on Stockfish but used for problem solving</p>
<p>SimpleEval: as I know also built on Stockfish, uses only material counting (1, 3, 3, 5, 9) as evaluation</p>
<p>Boris-Trapsky: plays not the strongest position, but position in which a person is likely to make a mistake</p>
<p>Maia: try to play like human</p>
<p>There are also different game modes in Komodo, but they are not free.</p>
<p>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.</p>
 10075: <p>Dr Tom Murphy examines 30 interesting chess algorithms in a joke paper for SIGBOVIK 2019, which can be read here:</p>
<p><a href="http://tom7.org/chess/weak.pdf" rel="nofollow noreferrer">http://tom7.org/chess/weak.pdf</a></p>
<p>Among them are strategies such as:</p>
<ul>
<li>&quot;worstfish&quot;, which plays the worst move according to Stockfish</li>
<li>Various neural networks strategies, some of which are given modified views of the board</li>
<li>A strategy that plays the move that minimises the number of resulting legal moves for the opponent</li>
<li>&quot;equalizer&quot;, which prefers to move pieces that have been moved the fewest times</li>
<li>Less popular classical chess engines such as Topple and ChessMaster for the NES</li>
</ul>
<p>A video version of the paper is also available: <a href="https://www.youtube.com/watch?v=DpXy041BIlA" rel="nofollow noreferrer">https://www.youtube.com/watch?v=DpXy041BIlA</a></p>
 17004: <p>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: <a href="https://chess.massimilianogoi.com/download/corchess/" rel="nofollow noreferrer">https://chess.massimilianogoi.com/download/corchess/</a></p>
<p>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: <a href="https://lichess.org/" rel="nofollow noreferrer">https://lichess.org/</a></p>
<p>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.</p>
<p>If you love to learn more about chess engines, my favorite website is <a href="https://chessengines.blogspot.com/" rel="nofollow noreferrer">https://chessengines.blogspot.com/</a></p>
<p>They also have a weekly free magazine that I highly recommend to you.</p>
<p>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: <a href="https://komodochess.com/" rel="nofollow noreferrer">https://komodochess.com/</a></p>
