EPPlus by: Jan Källman

A library to manage Excel spreadsheets, using OOXML.

Esprima by: Sebastien Ros

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

ExcelDataReader by: ExcelDataReader developers

Lightweight and fast library written in C# for reading Microsoft Excel files (XLS, XLSX).

ExcelNumberFormat by: ExcelNumberFormat developers

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

ExCSS by: Tyler Brinks

ExCSS is a CSS 3 parser for .NET. ExCSS makes it easy to read and parse stylesheets into a friendly object model with full LINQ support.

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.

Figgle by: Drew Noakes

ASCII banner generation for .NET

FirebirdSql.Data.FirebirdClient by: FirebirdSQL

Firebird ADO.NET data provider

Fizzler by: Atif Aziz Colin Ramsay

Fizzler is a W3C Selectors parser and generic selector framework for document hierarchies.

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.

FluentMigrator by: Josh Coffman Tom Marien

FluentMigrator is a database migration framework for .NET written in C#. The basic idea is that you can create migrations which are simply classes that derive from the Migration base class and have a Migration attribute with a unique version number attached to them. Upon executing FluentMigrator, you tell it which version to migrate to and it will run all necessary migrations in order to bring your database up to that version. In addition to forward migration support, FluentMigrator also supports different ways to execute the migrations along with selective migrations called profiles and executing arbitrary SQL.

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.

Fluxor.Blazor.Web by: Peter Morris

A zero boilerplate Redux/Flux framework for Blazor

Fody by: The Fody Team

Extensible tool for weaving .net assemblies.