The Restricted Use Case Modeling (RUCM) approach is composed of a set of well-defined restriction rules and a new template, aiming to reduce ambiguity and facilitate automated analysis. Zen-RUCM is an RUCM-based framework to tackle the challenges of requirement specification in different application domains (eg, real-time systems) and from various requirement specification concerns (eg, variability). In this demonstration, we discuss an implementation of the Zen-RUCM framework with the focus on its lightweight design architecture and extension mechanism.(Demonstration video link: http://youtu. be/a8YZ_wuVxQg)