This system is a reliable way of meeting White's anti-Sicilian choice, as long as you don't mind an isolated queen's pawn, a position that can also arise from the French Defense.
1. e2e4  1... c7c5  2. g1f3  2... e7e6  3. c2c3  3... d7d5  4. e4d5  4... e6d5  5. d2d4  5... b8c6  6. f1b5 