Gazebo is a FICS chess interface written in C#, using Gtk# for the user interface. It is extremely extensible already, making use of the mono-addins library to allow nearly complete customization by addin authors.

Conjurer is a collection of my personal utilities for XNA Framework, which is primarily used for a games development.

Currently I'm using it in https://www.ohloh.net/p/digger-net project.

Garnet is a light-weight Ruby on Rails editor for Windows, written in C# 3.5. The main project pages are at http://garnet-editor.googlecode.com/.

Lokad Message Contracts DSL Sample (aka Mercenary) is a reference implementation that shows how to streamline .NET contract generation with Visual Studio.

This is useful for reducing development friction on projects that use CQRS, DDD, Event sourcing or rely on any other repetitive code that changes frequently....

HoboVM is a stack-based virtual machine written entirely in C#. The goal of the project is to create a scripting language and interpreter for programs written for the .NET, .NET Compact, or Mono frameworks. Currently it is capable of executing a custom assembly language stored on a virtual ROM, performing calculations and logic on a floating point stack, and swapping floats in and out of virtual RAM....

Looking for a way to display real time information in a GUI?,

NauckIT.Remoting is a small helper library to setup .NET remoting and publish or consume remote objects.

DrC# (DrCSharp) is an integrated C# development environment that supports interactive evaluation of expressions.

libanculus-sharp is a reusable utility library written in C#.

"Anculus" means servant in Latin, and that is exactly what the library does. It serves and helps you to easily and quickly write new applications. libanculus-sharp contains all the building blocks that you need to develop a good C# application....

Script# is a C# to JavaScript compiler that lets you use c#, Visual Studio and .NET tools to build HTML5 applications.