Drools
Drools is an open-source business rule management system (BRMS) and a production rule system that uses a rule-based approach to implement application logic. It provides a core Business Rules Engine (BRE), a web authoring and management environment called Business Central, and full runtime support for Decision Model and Notation (DMN). Developers use Drools to separate business logic from application code, enabling dynamic rule updates without redeploying applications.
Developers should learn Drools when building applications that require complex, frequently changing business rules, such as in finance for fraud detection, insurance for policy underwriting, or e-commerce for pricing and promotions. It is particularly useful in scenarios where non-technical stakeholders need to modify rules independently, as Drools allows rules to be written in a human-readable format and managed through a GUI, reducing development overhead and improving agility.