Higson.io - Hyperon is a BRMS, that was created with very large decisions and hyper-performance in mind. It stands out with the concept of the business domain which organizes the whole configuration in easy to manage way.
ILOG JRules - ILOG JRules is a business management system to allow developers and businesses to easily build and deploy a rule-based application that automates variable and fine-grained decisions.
OptaPlanner - Mathematical optimization software
Corticon - Progress Corticon Business Rules Engine helps organizations of all kinds make faster decisions by managing the rules that drive business processes.
Simple Rule Engine - DotNet simple BRMS XML rule engine
InRule - InRule is a cloud-ready business rule management platform that allows you to change business rules and decisions in the application without requiring JavaScript.