Antechinus A programmer's editor that supports color-coded syntax of the C# programming language. By C Point Pty Ltd. http://www.c-point.com/csharp.htm

HTML-Kit Highly customizable free C# editor. Includes syntax highlighting and lookup of online and offline help references. http://www.chami.com/html-kit/

HKPGEN Plugins Generator Visually design plugins for HTML-Kit and automatically generate source code in .NET C# http://www.chami.com/html-kit/devtools/

OpenGL for C# Provides C# wrapper for OpenGL & SDL along with some tools. http://csgl.sourceforge.net/

db4o An object database written in C# for the .NET platform. Also exist Java version. http://www.db4o.com/

Improve C# plugin for Eclipse Free open-source plugin for Eclipse (itself a free and open-source development environment) with syntax highlighting, content assistant (intellisense for C# keywords), and ability to compile code from within the IDE. http://www.improve-technologies.com/alpha/esharp/

Free Compiler Writing Tools Provides C# source for tools written in the tradition of lex and yacc, redesigned in an object-oriented way. By Malcolm Crowe. http://cis.paisley.ac.uk/crow-ci0/#research

Mentalis.org A collection of classes written in C# and VB.NET. http://www.mentalis.org/news/

Xceed Dot NET Products C# zip and streaming compression components for the Microsoft .NET framework. http://www.xceedsoft.com/products/ZipNet/

DotGnu Portable .NET An open-source C# compiler and libraries. http://www.southern-storm.com.au/portable_net.html

Sharp Develop Free C# editor. http://www.icsharpcode.net/OpenSource/SD/Default.aspx

C# Refactory A refactoring, metrics and productivity add-in for Microsoft Visual Studio.NET. http://www.xtreme-simplicity.net/csharprefactory.html

PocketProd The PocketNerd Productivity Tool, an add-in for Visual Studio.NET provide a simple, flexible way of extending the Visual Studio.NET IDE to increase developer productivity. http://www.pocketnerd.net/PocketProd/ASPX/Home.aspx?documentID=531D8580-B26E-4AAD-9046-A44BD6F31D3B

RapTier A template-based C#, VB.NET, and SQL code generator for multi-tier development. [Shareware] http://www.sharppower.com/

Instant C# Convert VB.NET code to C# code at the project and code snippet levels. Description, sample screenshots, and ordering information. By Tangible Software Solutions Inc. http://www.tangiblesoftwaresolutions.com/

eXtensible C# Provides attribute-based declarative assertions, partial based code verification and obfuscation for C#. Free download. http://www.resolvecorp.com

D4Modelizer A C# code generator. It produces code from a datasource and add managing persistance methods (Add/Modify/Remove) and create Visual Studio Project. It is easy and free. http://www.d4modelizer.com

Nini A software configuration library written in 100% C# for the .NET Framework. This software contains a concise API for abstracting the access of multiple configuration types: INI, .NET config files, registry, XML files, and command-line options. [Open source, MIT License] http://nini.sourceforge.net/

C-Sharpener For VB A Visual Studio addin that converts VB.Net projects to C# projects. [Commercial, free conversion service for open source projects] http://www.elegancetech.com/csvb.aspx

MonoDevelop A project to port SharpDevelop to Gtk#. http://www.monodevelop.com/