Chess accounts for the bulk of Computer tournaments and attracts the most substantial effort. The top programs now play at a level substantially above human World Champions, the current strongest being Hydra. One of our old Chess engines is based on the Chess System Tal program, authored by Chris Whittington. This unusual program is renowned for its strong human style, resembling that of the former World Champion Mikhail Tal. Its strength was in the creation of positions with great tactical complexities, as the World Champion Petrosian remarked "I know what to do in the positions that Tal creates, but I do not know how to create them". However AI Factory also has its own newer in-house chess program "Treebeard
", authored by Jeff Rollason. This was chosen by Microsoft
for their MSN Chess and a later version of this is by far the most popular chess program on Android, ranking #10/#19 UK/US among Brain & Puzzle apps, where the next highest chess is ranked is #45/#81. Treebeard also has an unusual human-like play style through its unusual static lookahead and probability-based tree search. This gives a strong human-like quality to the games, making it an agreeable opponent. However the engine is no slouch as is widely praised for its strength.