Top 20 NuGet rule-engine Packages

Simple, clean, and object-oriented way to create and execute business rules in .NET
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
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.
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.
The Micro Rule Engine is a small(As in about 200 lines) Rule Engine that allows you to create Business rules that are not hard coded. Under the hood MRE creates a Linq Expression tree and compies a rule into an anonymous method i.e. Func<T bool>