ErrorOr by: Amichai Mantinband

A simple, fluent discriminated union of an error or a result.

Esprima by: Sebastien Ros

Standard-compliant ECMAScript 2022 parser (also known as JavaScript).

ExcelDataReader by: ExcelDataReader developers

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

ExcelDataReader.DataSet by: ExcelDataReader developers

ExcelDataReader extension for reading Microsoft Excel files into System.Data.DataSet.

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

Expecto by: Henrik Feldt and contributors

Advanced testing library for F#

Extended.Wpf.Toolkit by: Xceed

Extended WPF Toolkit is the number one collection of WPF controls, components and utilities for creating next generation Windows applications. Provides 48 controls, all offered under the Xceed Software Inc Community License. v5.1 provides 12 bug fixes and improvements. Documentation, source, and discussions are hosted on Github at https://github.com/xceedsoftware/wpftoolkit. Check out the Plus Edition to support the project, get more controls and features, and work with a version a few releases ahead of the free releases.

Fable.Core by: Alfonso García-Caro Núñez

Fable Core Library

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.

Fare by: Nikos Baxevanis

.NET port of dk.brics.automaton - Project Fare is an effort to bring a DFA/NFA (finite-state automata) implementation from Java to .NET. There are quite a few implementations available in other languages today. This project aims to fill the gap in .NET.

fasterflect by: Buu Nguyen, Morten Mertner, Bernard Dijk

.NET library that improves your productivity and application performance when performing reflection operations. It allows you to perform metadata lookup and reflection invocation intuitively while achieving greater performance than the built-in .NET Reflection.

FastExpressionCompiler.src by: Maksim Volkau

FastExpressionCompiler is 10-40x times faster than Expression.Compile()

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.

FFmpeg.AutoGen by: Ruslan Balanukhin

FFmpeg auto generated unsafe bindings for C#/.NET and Mono.

Firebird.v2-5-x.Embedded by: rene hankel

necessary firebird embedded dll's for .NET applications from firebird release v2.5.6.27020 (x86 and x64 depending by project settings) ATTENTION - not working with clickonce applikations(the files will be not part of the clickonce paket :/)

Fixie by: Fixie, Patrick Lioi

Ergonomic Testing for .NET

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, MSTest3, MSTest4, 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.