There are very few Rules Management sytems out there in the market either commercial or open-source. The top ones (commercial) are Blaze and ILog, though there are others too like Pega, Yasutech, Hailey, but I am not sure about them since I have worked primarily on the first two. In the open-source space the only when I think which offers anything close to a Rules management system is "mandarax".

This is a critical area which is still open and unanswered. I have worked on business rules engine since last 4 years and rules management is one of the major contributors to the success and failure of any project using a business rules apparoach to application development.

Thanks.