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

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

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

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/

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

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/

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/

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

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

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

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/

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

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

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

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

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

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/

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

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

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