A simple ASP.NET MVC implementation of the NuGet back-end gallery and web APIs.
NHibernate is a mature, open source object-relational mapper for the .NET framework. It is actively developed, fully featured and used in thousands of successful projects.
Fluent Migrator is a migration framework for .NET much like Ruby Migrations.
Incredibly simple real-time web for .NET
Nancy is a lightweight, low-ceremony, framework for building HTTP based services on .Net and Mono
git-tfs is a two-way bridge between TFS and git, similar to git-svn.
The AWS SDK for .NET enables .NET developers to easily work with Amazon Web Services.
LibGit2Sharp brings all the might and speed of libgit2, a C native Git implementation, to the managed world of .Net and Mono.
This SDK allows you to build Windows Azure applications that take advantage of Azure scalable cloud computing resources.
The .NET framework. Recently open sourced by Microsoft.
Cake (C# Make) is a cross platform build automation system.
Humanizer meets all your .NET needs for manipulating and displaying strings, enums, dates, times, timespans, numbers and quantities.
The package manager for Windows
Orleans - Distributed Virtual Actor Model
A cross-platform library for the processing of image files; written in C#
Binding business requirements to .Net code