user1656: Why buy Houdini (or Rybka) if Stockfish is essentially as powerful and also is free?
Are there special features or a nicer GUI? Can't those features be implemented within the Stockfish engine?

user1671: I use Critter 1.6a with the Jose database (Macintosh version), I also use Komodo 5.1
and Stockfish for the same database. They all give somewhat varied evaluations and continuations unless there are forcing lines. I have been following the following tournament: http://chessbomb.com/site/  nTCEC Season 2 Stage 2 , the field consists of 19 engines , and Rybka and Houdini are not in the lead! (Houdini and Rybka are equal 9th place.) An engine, Gull 2.2 which I had never heard of, and which is free, is in the lead,(for now).  
As far as GUIs are concerned,on a windows computer either Arena (free) or Aquarium will run engine competitions, both have their share of bugs and features. 

user1485: Some interesting quotes from Maxime Vachiere-Lagrave in New in Chess (2011/5):
About Rybka:

... Obviously, each new version improved the engines a little bit, but to my mind the general structure of the programmes remained largely the same. This routine was busted in 2006 with the appearance of Rybka at the highest level. Its main added value compared to the other available engines was an improved assesment function, which made it much more pleasant and actually more efficient to work with. It was simply much more natural and better adapted to the human way of thinking.

About Stockfish:

To be truthful, I had hardly heard of Stockfish when it appeared, and had hardly ever used it. It is evidently the fastest software around, but to my mind, its assessment function is sometimes back to slightly inhuman.

About Houdini:

In comparison, the latest newborn, Houdini, is a bit depressing, simply because of this 'equation': the truth x 2 = 1. From the discussions I have had, I can only guess that most top players are now using it as their main engine. The really astonishing thing is how resourceful it is. And contrary to other engines it can, even in what looks like really difficult positions, give an equal assessment, which it backs up with the moves it plays afterwards, which is simply amazing. 


1656: <p>Why buy Houdini (or Rybka) if Stockfish is essentially as powerful and also is free?</p>

<p>Are there special features or a nicer GUI? Can't those features be implemented within the Stockfish engine?</p>
 1671: <p>I use Critter 1.6a with the Jose database (Macintosh version), I also use Komodo 5.1
and Stockfish for the same database. They all give somewhat varied evaluations and continuations unless there are forcing lines. I have been following the following tournament: <a href="http://chessbomb.com/site/">http://chessbomb.com/site/</a>  nTCEC Season 2 Stage 2 , the field consists of 19 engines , and Rybka and Houdini are not in the lead! (Houdini and Rybka are equal 9th place.) An engine, Gull 2.2 which I had never heard of, and which is free, is in the lead,(for now).  </p>

<p>As far as GUIs are concerned,on a windows computer either Arena (free) or Aquarium will run engine competitions, both have their share of bugs and features. </p>
 1485: <p>Some interesting quotes from Maxime Vachiere-Lagrave in New in Chess (2011/5):</p>

<p>About Rybka:</p>

<blockquote>
  <p>... Obviously, each new version improved the engines a little bit, but to my mind the general structure of the programmes remained largely the same. This routine was busted in 2006 with the appearance of Rybka at the highest level. Its main added value compared to the other available engines was an improved assesment function, which made it much more pleasant and actually more efficient to work with. It was simply much more natural and better adapted to the human way of thinking.</p>
</blockquote>

<p>About Stockfish:</p>

<blockquote>
  <p>To be truthful, I had hardly heard of Stockfish when it appeared, and had hardly ever used it. It is evidently the fastest software around, but to my mind, its assessment function is sometimes back to slightly inhuman.</p>
</blockquote>

<p>About Houdini:</p>

<blockquote>
  <p>In comparison, the latest newborn, Houdini, is a bit depressing, simply because of this 'equation': the truth x 2 = 1. From the discussions I have had, I can only guess that most top players are now using it as their main engine. The really astonishing thing is how resourceful it is. And contrary to other engines it can, even in what looks like really difficult positions, give an equal assessment, which it backs up with the moves it plays afterwards, which is simply amazing. </p>
</blockquote>
