Rybka 4 Chess Playing Software For years Rybka has been the uncontested number one in computer chess. Now the new Rybka 4 plays even more aggressively and more tactically, with better understanding of the attack on the King. Rybka 4 is more precise and reliable than its predecessor. Rybka 4 contains a database of 1.5 million games and includes Classic membership for Playchess. com for one year. Rybka 4 is a UCI engine, with 32 and 64-bit versions included in the package. Rybka can be made the default engine in ChessBase 10.