FluentValidation by: Jeremy Skinner

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

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.

Glob by: Kevin Thompson <kevin@theautomaters.com>

A C# Glob library for .NET and .NET Core.

Fhir.Metrics by: Martijn Harthoorn

Conversion system for physical units, with UCUM implementation - The Unified Code for Units of Measure

FastEndpoints by: FastEndpoints

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

ExcelNumberFormat by: ExcelNumberFormat developers

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

FastExpressionCompiler by: Maksim Volkau

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

Elmah.Io.AspNetCore by: elmah.io

An elmah.io provider for ASP.NET Core

Flurl.Http by: Todd Menier

A fluent, portable, testable HTTP client library.

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.

Flurl by: Todd Menier

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

Flurl.Http.Xml by: Luk Vermeulen

XML extensions to Flurl.Http

Google.Protobuf by: Google Inc.

C# runtime library for Protocol Buffers - Google's data interchange format.

EPPlus by: Jan Källman

A library to manage Excel spreadsheets, using OOXML.

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.

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.

FastEndpoints.Swagger by: FastEndpoints

Swagger support for FastEndpoints.

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.

Elmah.Io.Client by: elmah.io

.NET client for communicating with the elmah.io REST API

DotNetAnalyzers.PublicApiAnalyzer.Unstable by: Sam Harwell et. al.

An analyzer for packages with public APIs.