Rybka 4 Chess Playing Software PLUS Rybka 4 Opening Book - ChessBase Get the World Computer Chess Champion Rybka 4 PLUS the Rybka 4 Opening Book! Two chess software programs for one low price: Rybka 4 chess playing engine and a "book database" to make it stronger. Rybka 4 contains a database of 1.5 million games and includes Classic membership for Playchess.com for one year. The Rybka 4 opening book is a high-class compilation of opening theory. The Rybka 4 Book includes 17 million positions and over 700,000 games.