If you are a chess player you will need a good chess engine. But 1. Not to play against!!! It is bad to pit yourself against players that are wayyy too good for you to ever beat, chances are if you are a 1500 elo club player, you don’t stand a chance of defeating Stockfish engine in hardly any equal settings. (Starting with equal material from the starting position, and equal time controls). You need to play other 1500 elo players and generally within a couple hundred elo of yours so you have a chance to grow and learn at chess and improve your game and not rack your brain!
Here I will mention a few that deserve mention and that I have specifically used and links to find them. Keep in mind links sometimes do expire and engine builders sometimes let their webhosting expire and end up moving domains and whatnot. So when in doubt just do a little bit of searching on bing.com or google or Yahoo!
Numpty is a chess engine I had to hunt down, primarily because at the time it was one of the weakest UCI chess engines. (~2012). I wanted to have an engine that I could beat so that I was learning how to defeat an actual chess AI opponent which never comes easy! At the time Numpty was rated about 1200 elo to about 1400 elo which is why it would be fun to play against being that I am roughly in that elo rating, approx club player 1600 elo in Tournament chess against human players in long time controls.
Playing a few games against numpty I had about a 50/50 chance of winning given I could use takebacks now and then maybe more.
In the last couple years Numpty has been improved and debugged better by it’s author and is now ranked about 1700 to about 1900 elo. If you want the old Numpty with the imperfections it originally had you might have to do a little bit of Googling (internet searching with a search engine of your choice. Specifically Numpty_DD is the binary that I still have from 2013.
Official download: https://stockfishchess.org/download/
Stockfish developement versions: to current and best: http://abrok.eu/stockfish/
Currently, the two best engines are Komodo and stockfish, and in high end Chess championships and Tournaments they keep playing leapfrog, replaces each other as #1, or #2 in AI/computer chess.
Stockfish is also available for iOS as smallfish or search stockfish on the app store and as well available for Android devices under the same name.
Stockfish is a very good engine for analysing very tough positions and endgames that are from your real games so you can learn from your mistakes, also you can ask the gui you are using it with to diminish it’s playing strength to a certain elo, so it can mulate a weaker player as well.
I find it most handy for analysis of positions and my own games and other peoples games. It has multiPV so it can show you several principal variations and rank them from best to worst.
Chenard is a powerful engine that I can remember playing as far back as 1999 ad, on old 400 MHz Pentium 2 computers in the college library, I could win sometimes, but after chess burn out set in I would have to start using takebacks. It was lots of fun!
Today you don’t have to download their tacky interface you can just use the UCI plugin of the engine in your favorite interface/gui whether you use Arena (free), Tarrasch (free), or Fritz/Shredder chess interface. Another fun thing to do is pit it against similar ranked engines then look at the games and the analysis of the games or run it on your pet openeing to see if it finds certain nuances!