Some years ago one Blogger selected 100 positions from Fischer's games and tested them to see which ones played the most like him and the top engines selected only about 60-65 percent of his moves. But, those engines are no longer available. In any case, most of the humans we play aren't going to select 65 percent of Fischer's moves, so we are actually looking for something else.
The Vitruvius engine's site says, “Vitruvius is built on the skeleton structure of the free Ippolit programs (RobboLito, Igorrit, IvanHoe) from which it inherits certain characteristics and peculiarities. It is however a chess engine in its own right exhibiting a very original style of play with a highly speculative tendency. Thanks to its finely tuned positional vision, Vitruvius shows a readiness to sacrifice a pawn or two, the exchange and sometimes even a whole piece, for purely positional compensation…Vitruvius’ goal is to promote powerful, human-like-play in order that players of all strengths and levels can benefit from its use in their preparation for their over the board engagements. The current version has been used by strong IMs in their preparation, training and study and it has proved itself time and again to be a very helpful and ‘unforgiving’ sparring partner.” I don't own this engine which sells for about $28 (25 Euros).
Another commercial program that claims to play like a human is HIARCS which, according to the site, plays “with realistic human-like handicap levels for players from beginner to Grandmaster...opponents to match your ability.” Again, I have never owned HIARCS; it sells for about $60 (54 Euros).
I have the Fritz 12 GUI and so I was interested in seeing how it works for practice games with the Stockfish 6 engine. Fritz has modes for: Handicap, Sparring, Friend.
In the Handicap Mode you can set a base playing strength in the Elo range of 1250 to 2125 plus determine a number of other characteristics such as attacking the king, trading pieces at every opportunity, which side of the board it should seek play on, severity of its blunders, etc.
In the Sparring Mode the claim is 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...or so it says. In the Sparring Mode the engine did make a tactical error that lost a piece and it warned me when it made the error. This is a feature I really didn't care for because in a real game you don't get any such notifications. Besides, in one of the Blitz games where I supposedly failed to find the best move to its tactical mistake the notification was just plain wrong. Examining the game afterward, it turned out my move was the best.
In the Friend Mode the program attempts to automatically adjust its level to yours. When you start, it asks you for your “Handicap”. After a few games it attempts to adjust your handicap to reflect your real playing strength. The smaller your handicap, the stronger you are. I did not care for this mode either. I set the handicap at zero and the three games I played against it were drawn. It seemed that if I did nothing but shuffle pieces and trade at every opportunity, so did the engine.
I got what appeared to be the best results playing it in the Handicap Mode. I selected 1800 Elo and left all the settings at the default which is right in the middle of the sliding scale. I won all three game games and the engine did seem to play a decent game with no stupid errors. I also played a couple of games at the lowest setting of 1225. I'm not sure how well 1200 players play these days, but it did play at a considerably lower level than at the 1800 level. In fact, in one game I deliberately let it play an ending where it had a R+B against my B and it failed to win. At the 2125 setting I lost one and drew one.
If you don't have Fritz, both SCID for PC and Arena allow you to adjust the engine playing strength, but I am not sure which Fritz mode the adjustments might correspond to. At least in Fritz using the handicap mode seems to be a reasonable try at duplicating human play for practice. Stockfish also seemed to be the best engine.