Enums.NET by: Tyler Brinkley

Enums.NET is a high-performance type-safe .NET enum utility library

EPPlus by: Jan Källman

A library to manage Excel spreadsheets, using OOXML.

EPPlus.Core by: Vahid Nasiri

EPPlus.Core is an unofficial port of the EPPlus library to .NET Core.

Esprima by: Sebastien Ros

Standard-compliant ECMAScript 2016 parser (also popularly known as JavaScript or ES6).

ExcelNumberFormat by: ExcelNumberFormat developers

.NET library to parse ECMA-376 number format strings and format values like Excel and other spreadsheet softwares.

ExtendedNumerics.BigDecimal by: https://github.com/AdamWhiteHat

Arbitrary precision decimal class

FakeItEasy by: Patrik Hägne FakeItEasy contributors

It's faking amazing! The easy mocking library for .NET that works great in C# and VB.NET alike. No need to know the difference between a stub, a mock or a spy, everything's a fake! The easy to use, refactoring friendly API makes faking a breeze.

FastEndpoints by: FastEndpoints

A light-weight REST Api framework for ASP.Net 6 and newer that implements REPR (Request-Endpoint-Response) Pattern.

FastMember by: Marc Gravell

In .NET reflection is slow... well, kinda slow. If you need access to the members of an arbitrary type, with the type and member-names known only at runtime - then it is frankly hard (especially for DLR types). This library makes such access easy and fast.

FastMember.Signed by: Marc Gravell

In .NET reflection is slow... well, kinda slow. If you need access to the members of an arbitrary type, with the type and member-names known only at runtime - then it is frankly hard (especially for DLR types). This library makes such access easy and fast.

FirebirdSql.Data.FirebirdClient by: FirebirdSQL

Firebird ADO.NET Data provider

FluentAssertions by: Dennis Doomen Jonas Nyrup Xceed

A very extensive set of extension methods that allow you to more naturally specify the expected outcome of a TDD or BDD-style unit tests. Works with .NET Standard 2.0 and higher, .NET Framework 4.7 and higher and .NET 6 and higher. Supports the unit test frameworks MSTest2, NUnit3, NUnit4, XUnit2, XUnit3, MSpec and TUnit. IMPORTANT: This version is free for open-source projects and non-commercial use, but commercial use requires [a paid license](https://xceed.com/products/unit-testing/fluent-assertions/). Check out the [license page](LICENSE) for more information.

FluentNHibernate by: James Gregory and contributors

Fluent, XML-less, compile safe, automated, convention-based mappings for NHibernate.

FluentValidation by: Jeremy Skinner

A validation library for .NET that uses a fluent interface to construct strongly-typed validation rules.

FluentValidation.AspNetCore by: Jeremy Skinner

AspNetCore integration for FluentValidation

Fluid.Core by: Sebastien Ros

Fluid is a template engine based on the Liquid markup, with focus on performance and .NET programming patterns.

Flurl by: Todd Menier

A fluent, portable URL builder. To make HTTP calls off the fluent chain, check out Flurl.Http.

Flurl.Http by: Todd Menier

A fluent, portable, testable HTTP client library.

Fody by: Fody

Extensible tool for weaving .net assemblies.

Fractions by: Daniel Mueller

The fraction data type consists of two BigInteger values for numerator and denominator. It implements various operations (addition, subtraction, multiplication, division and remainder) with operator overloads.