PlayMaker is a popular visual scripting tool for the Unity game engine which is used in countless games including one of my favorites! Hollow Knight. I developed an action that evaluates expressions for branching which is shipped with PlayMaker.
The action has a custom user interface which performs real-time syntax and error checking as the expression is being typed. This is powered by a simple recursive decent parser. The syntax supports various standard expression operators and allows variables to be referenced in one of two ways. Variables are accessed via the API that PlayMaker exposes.
Action documentation: https://hutonggames.fogbugz.com/default.asp?W1226