Arimaa is a two-player board game invented by Omar Syed, a computer engineer trained in artificial intelligence. Inspired by Garry Kasparov's defeat at the hands of the chess computer Deep Blue, Syed wanted to design a new game which would be difficult for computers to play well, but would have rules simple enough for his four-year-old son Aamir to understand. In fact, "Arimaa" is "Aamir" spelled backwards plus an initial "a." In 2002 Syed published the rules to Arimaa and announced a $10,000 prize, available through 2020, for the first computer program to win matches against top-ranked human players. David Wu's bot Sharp accomplished this in 2015, but the result was invalidated due to side bets placed by participants. The Challenge thus remains in effect through 2020.
Arimaa was specifically designed so that it could be played using a chess set—an 8×8 board is used, and each player has sixteen pieces, in a 1-1-2-2-2-8 distribution. It can also be played on-line at the arimaa.com gameroom. In 2009, Z-Man Games began producing a commercial Arimaa set. Only one face-to-face tournament has taken place, but about 900 games are played on-line every week. Omar Syed hosts four events per year in the gameroom:
- The World Championship is a tournament for human players which typically runs from January to March. Jean Daligault of France has won the championship six times, in 2007, 2009, 2010, 2011, 2013, and 2014. On a scale of ratings comparable to Elo chess ratings, Daligault is rated near 2400.
- The Computer Championship matches the top Arimaa bots in an elimination tournament. David Fotland's program Bomb placed first from 2004 to 2008. Jeff Bacher's Clueless prevailed in 2009. Mattias Hultgren's Marwin won in 2010 and 2012. David Wu's Sharp triumphed in 2011, 2014, and 2015. Ricardo Barreira's Ziltoid was victorious in 2013.
- The Arimaa Challenge took place following the Computer Championship. The top two bots were available to play for a period. The one that achieved the better record against humans who play at least two games against both bots advances to the Challenge. The bot faced three ultimate human defenders, who were selected beforehand and hadn't played in the initial round. If this bot could defeat all three human defenders, its developer would the $10,000 prize. Humans dominated until 2015, when Sharp defeated all three human defenders (though Sharp's victory was subsequently voided because of bets.)
- The yearly Postal Mixer begins in April and ends around October. The emphasis of this tournament is participation, rather than determining a champion. The objective is to advance the frontiers of strategic knowledge, as well as to spread around existing knowledge by pairing people to a variety of opponents.
In addition to these events, the 1st Arimaa Online Festival was organized for 11 September 2010. This event included Arimaa matches, a strategy workshop, and an interview with Omar Syed.
United States Patent number 6,981,700 for Arimaa was filed on the 3rd of October 2003, and granted on the 3rd of January 2006. Omar Syed also holds a trademark on the name "Arimaa". Syed has released an experimental license called "The Arimaa Public License", with the declared intent to "make Arimaa as much of a public domain game as possible while still protecting its commercial usage". Items covered by the license are the patent and the trademark.