Several fuzzers are available in the marketplace right now. Hailstorm and eEye's CHAM are commercial fuzzers. Greg Hoglund's Blackhat briefings slides are also worth a read if you want to dig further into this kind of technology. Many people have also written their own fuzzers, using data structures similar to SPIKE. If you plan to write your own, we suggest writing it in Python (if SPIKE was ever rewritten, it would no doubt be in Python). In addition, various talks at Blackhat on SPIKE are available from the BlackHat conference media archives.