SugaR XPrO (+0−18=14)
Komodo 11.2 (+0−15=18)
Stockfish 8 (+0−10=22)
Often when you artificially lower their strength engines don't play even close to the way humans do. However, Booot seems to have a human-like style and is an interesting practice partner. Over the holiday I was playing around with some of the engines I never use, but are installed on my Fritz GUI: Andscacs, Booot, Giraffe, McBrain, Roce, SmarThink, Symphysodon and Zappa.
I played a bunch of 10 minute games against them in the Sparring Mode. In this mode the program plays a reasonably strong game, but at the same time makes tactical errors. If the program finds a move that allows the opponent to gain a tactical advantage in a clever way, it will play that move. It is a very realistic human style, the kind you encounter in a chess club. You can select the grade of difficulty of the tactics: Very easy for players with an Elo of around 1400 and usually involves finding forks and two move combinations. Normal is meant for players between 1700 and 1900, and very hard is for players from 1900 and, so it says, all the way up to GMs.
I also experimented with playing it in the handicap mode. In this mode you can adjust playing strength from 1375 to 2300, the blunder range, attack on the king, King's defense, Piece placement, P-structure, mobility, canter control, piece trading, variety of openings ans piece play. I left everything at the mid-range setting (default) and adjusted the playing strength to 2100. The problem with this is that engines will often make a blunder at some point, but for most of the game play at GM strength.
But, using one of the weaker engines in the Sparring mode, I could, to some extent, overcome these problems. The engine that proved to be the most fun was Booot. It did play reasonably human-like especially in the Sparring mode as evidenced by the game below. I think it might make a good practice engine because it's moves did seem reasonably human-like. Version 6.2 can be downloaded from HERE.