NSpecification (nuget): NSpecification is the most complete library for the Specification pattern and it's grounded on the Domain-Driven Design principles. Provides interface, abstract and a generic specification, composable, supports operators. This is probably the most fluent and least verbose library. Specifications can be composed with real operators (&, |, !, ==, !=). They are interchangeable with Expression<Func<T, bool>> and Func<T, bool> and can be combined directly with boolean expressions. Check the tutorial in the GitHub.
Keywords: DDD|Specification