Are you a major enterprise-sized organization with a lot of rules and lots of programming disciplines to worry about? Then there’s really Fair Isaac Blaze Advisor and ILOG JRules – and then there’s everyone else. Those two are always noted as the major pure-play rule vendors. Pegasystems is the other big name in rules, but they concentrate more on combining rules and BPM into a single package than they do on selling stand-alone rules packages. JESS is the historical favorite in the techie world for getting into the game, because you can download their language and execution engine for free to start learning it and writing basic systems. But it’s a complex language and clearly made for the academic rules crowd. After those, you’ve got an awful lot of niche players and folks putting together their offerings.
If you are wondering if the big boys… Microsoft and IBM are in the game? They have each flirted with offerings in this area (I know of several different rules offerings by IBM, for instance) but have not yet come out with anything serious. It turns out it takes a lot of dedicated development, support, and marketing to push a full rules product.