Web Rule Engine / Expression Builder

Preface:

I see a similar question has been asked and closed 4 years ago. I am looking for any new development or guidance on this issue

Overview:

I was wondering if any new rule/expression building interfaces have been open sourced (preferably in GWT or Javascript/Node). I am looking for something similar to scratch but significantly less robust. This seems like common front end quandary. I've also noticed some really awesome engines like nools that are now available. Any guidance on how to tackle an expression building interface similar to scratch would be greatly appreciated.

Current Direction:

I've been looking into rule engines, abstract trees, and state machines (rete algorithm).