You may evaluate the latest OpenRules Decision Manager for free: LINK

WhatsNew:

2024 Jan. Release 10.1.0 comes with essentially enhanced RuleSolver and RuleDB, plus various improvements of the core product.
2023 Sep. OpenRules presented “Declarative Decision Modeling with Rule Solver" at DecisionCAMP
2023 Jul. Release 10.0 essentially changes the internal structure of the generated Java code to support newly introduced OpenRules features such as dynamically defined decision variables with the qualifier “Of”, advanced “for-each” loops, SpringBoot 3, JDKs versions 1.8, 11, and 17+ with Jakarta, and more.

This OpenRules guide
is available from Amazon.
OpenRules Books are
accompanied by free
evaluation software
available from here

WhatTheySay:

Forrester Research, Inc.

"OpenRules have the most-aggressive approaches to business-expert authoring and typically requires less developer support than IBM ODM, FICO Blaze Advisor, and Red Hat Drools."
Market Overview: Business Rules Platforms