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/c_sharp_editor.php

Blue Ink
   A C# application generating software program that decrease development time for database enabled web applications. [Commercial]
   http://www.blueink.biz

C# Rapid Development Kit
   A series of advanced collections and more than 50 generic algorithms that are designed to complement, not replace, the basic features found in the .NET Framework. [Commercial]
   http://www.recursionsw.com/Products/csharp.html

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

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

Clover.NET
   Clover.NET provides code coverage for .NET projects. Measures method, statement and branch coverage. reports in XML, HTML or via Visual Studio Plugin. A suite of NAnt tasks are provided. [Free for Open Source and Non-commercial projects]
   http://www.cenqua.com/clover.net/

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

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

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/

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/

MonoDevelop
   A project to port SharpDevelop to Gtk#.
   http://www.monodevelop.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 sourc
   http://nini.sourceforge.net/

OCL (Open CLI Library)
   Intel Labs C# implementation of portions of the CLI (Common Language Infrastructure) runtime library as defined in the draft ECMA CLI specification.
   http://sourceforge.net/projects/ocl/

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

Prof-It for C#
   A standalone profiler for C# that measures execution frequencies for each statement while keeping the instrumentation of the source code to a minimum. [Open source, GPL]
   http://dotnet.jku.at/projects/Prof-It/

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

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

TCDesigner Code Generator
   Generate C# source code and SQL Server stored procedures for entire data tier. Excellent performance without DataAdapters.
   http://www.tcdesigner.com

Tangible Architect
   Generates the data access layer for C# application and the database schema from within Visual Studio.NET .
   http://www.tangiblearchitect.com/

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

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