Top 20 NuGet rule-engine Packages

Create-compile-execute simple business rules at runtime. Built using Expression Tree; once compiled, rule can be executed over and over... with almost next to nothing execution time
Rule factory to create expression tree based rules. Rules Factory can help create rules; since there may be too many details to keep track for a complex rule.
A simple expert system shell implemented in C# that supports forward and backward chaining, capable of asking more questions when it fails to reach conclusion.