Top 20 NuGet functional Packages

Combinatorial Monads for Result, Task, Linq and IAsyncEnumerable. Inspired by Scott Wlaschin and railway oriented program design principles. Uses latest features of C# to adopt new paradigms based on functional monadic design. Retains minimalist design. Easy learning and migration curve.
C# implementation of the functional Result monadic type.
NitroBolt.Functional
https://github.com/khanage/Bearded.Monads
Functional Reactive Programming Library for .NET. https://github.com/jerometerry/potassium http://www.jerometerry.com/potassium/
A syntax sugar library for C++, especially providing LINQ-like ease for functional programming.
A C# extension library that allows users to compose and curry Func<> and Action<> delegate instances at runtime.
Types and extensions for declarative data transformations.
A functional switch statement based on code by Bart De Smet: http://bartdesmet.net/blogs/bart/archive/2008/03/30/a-functional-c-type-switch.aspx
Functional primitives for Unity3D - inspired by csharp-monads, Haskell & F#
Collection of simple pieces of reusable code designed such that dependencies aren't forced upon consumers of its packages. Package is shipped as source code.
Functional primitives for Unity3D - inspired by csharp-monads, Haskell & F#
ChainSharp provides wrappers in form of extension functions around C# keywords such as is and as to make them more chainable, and thus more readable.
CSharpFunctionalExtensions - functional extensions for C# Net 4.0 After install please update Microsoft.Bcl to 1.1.10 Nuget installs 1.1.8
Contains return types the reveal possiblities of executing code eg. Exceptional and Validation. Uses LanguageExt for some functional features.
Basic C# functional classes
Davenport is a CouchDB client for simplifying common tasks like get, list, create, update and delete. This package implements all of the functions from the original C# package, making it much more friendly to the functional programming style of F#.
HTTP extensions using Oxide.
Functional validation for C#
Provides fast and memory efficient alternatives to the collections in System.Collections.Immutable. Currently just includes SchematiqList as a replacement for ImmutableList.