|Original author(s)||Fabien Letouzey|
|Initial release||March 17, 2004|
|Stable release||2.3.1 / August 2, 2007|
|License||GNU General Public License and proprietary, freeware|
Fruit is a chess engine developed by Fabien Letouzey. In the SSDF rating list released on November 24, 2006, Fruit version 2.2.1 had a rating of 2842. In the CEGT rating list released on January 24, 2007, Fruit version 2.2.1 had a rating of 2776.
Until Version 2.1 (Peach), Fruit was free and open-source software subject to the requirements of the GNU General Public License and as such contributed much to the development in computer chess in recent years. Some people still work on the old source code and have created variations from the original Fruit.
Technical details of Fruit 2.1
Fruit uses the classical Negascout (principal variation search) algorithm with iterative deepening to traverse the game tree. It also uses the null-move heuristic. The original version used a simplistic evaluation function with a robust search. Later versions have improved evaluation functions. The board representation is distinct — Fruit uses a 16x16 board.
Although Fabien Letouzey's development of Fruit stopped in 2007 with version 2.3.1, the earlier open source 2.1 version provided the basis for many other programs.
Toga II is a derivative created by Thomas Gaksch. It has more chess knowledge, multi-processor support, and perhaps a better search algorithm. It is based on Fruit 2.1 and is free. The strongest version is Toga II 3.0, released on 23 March 2013 by Jerry Donald. Experimental versions of Toga II running on computer clusters have competed in the World Computer Chess Championship (WCCC). At about 80 ELO above Fruit 2.3.1, Toga II is the strongest Fruit derivative as of March 2014[update].
In 2008, forks of Toga II started to appear, like Grapefruit and Cyclone.
GambitFruit is another free derivative of Fruit 2.1, created by Ryan Benitez. It plays a more aggressive style and has more chess knowledge. GambitFruit also incorporates improvements from Toga II. Development of GambitFruit stopped in 2005.
GNU Chess 6.0 is based on Fruit 2.1.
Fruit Reloaded by Fabien Letouzey, Daniel Mehrmann and Ryan Benitez is an independent fork of Fruit 2.1 with a number of enhancements.
In June 2011, a lengthy investigation by the International Computer Games Association (ICGA) determined Rybka was plagiarized from Fruit and Crafty. The author of Rybka, Vasik Rajlich, refused to address the allegations against Rybka with the ICGA, instead preferring a ex post facto public interview conducted by Nelson Hernandez on July 4, 2011. Rajlich had previously said: I went through the Fruit 2.1 source code forwards and backwards and took many things. 
On the tenth anniversary of the start of Fruit development, Fabien Letouzey released a completely new engine, Senpai, making use of chess engine developments made in the intervening decade. It differs from Fruit in using bitboards and C++11's thread support for SMP.
||This article includes a list of references, but its sources remain unclear because it has insufficient inline citations. (April 2009)|
- "Team / History". fruitchess.com. Retrieved 2014-03-17.
- Letouzey, Fabien (March 17, 2004). "Fruit 1.0 UCI (with source code) now available". Computer Chess Club Archives. Retrieved March 18, 2014.
- Benitez, Ryan (August 2, 2007). "Fruit 2.3.1 released". talkchess.com. Retrieved March 19, 2014.
- Fruit Chess Engine by Fabien Letouzey
- "Custom engine selection". CCRL. Retrieved March 18, 2014.
- "Fruit Reloaded". Retrieved 2014-03-17.
- Doggers, Peter. "Rybka disqualified and banned from World Computer Chess Championships". Chess Vibes. Retrieved 29 June 2011.
- Hernandez, Nelson. "Another interview with Vasik Rajlich".
- "Interview with Vasik Rajlich (Dec 2005)".
- Official Fruit Homepage
- Official Fruit 2.3.1
- Fruit 2.1 source
- Official distribution web site (2.1 and below)