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 able to defeat a top-ranked human player in a match six games or longer. The prize has not yet been won.
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 was the Arimaa world champion five times, in 2007, 2009, 2010, 2011 and 2013. 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 every year from 2004 to 2008. Jeff Bacher's Clueless prevailed in 2009, Mattias Hultgren's Marwin in 2010, and David Wu's Sharp in 2011; Marwin repeated in 2012; and Ricardo Barreira's Ziltoid won in 2013.
- The Arimaa Challenge takes place following the Computer Championship. The top two bots are for a time available to play. The bot with the better record against humans who have played two games against each moves on to face three ultimate human defenders, who have been selected beforehand and prohibited from playing in the initial round. If this bot can defeat all three human defenders, its developer wins the $10,000 prize. So far, humans have dominated every challenge match.
- 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 has been 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.