Functionalsharp was created to bring some of the (nice) ideas from functional programming into C#. Also it was a personal training project examining the limits of what is currently possible with C#. If you have intrest in functional programming in the .NET world you can check out F#.
Functionalsharp has no external dependencies but makes use of Fody.NullGuard to make sure it never returns a null value/allows a null value to be passed unless explicitly specified.
See the docs for more information.