AddOn Studio for World of Warcraft is an open source development tool for building AddOns for World of Warcraft.

IDE for AjGenesis Code Generation.

IDE for assembler developing

"AutoIt Elements" wird eine speziell auf die Skriptsprache AutoIt zugeschnittene IDE.

You want something for free, go begging.

"Carcass" project makes it easier creating IDE-like applications similar to Microsoft Visual Studio Shell and SharpDevelop IDE. Its mission is to provide the flexible and extensible infrastructure necessary to create an IDE-based application in WPF with less efforts.

CLIDE .NET The Command Line IDE for .NET Because Code is just Code

Clone Detective is a Visual Studio package that allows you analyze your C# project for clones. A clone is region of source code that is duplicated.

Naja (a.k.a. Cobra IDE) is an Integrated Development Environment for the Cobra programming language (www.cobra-language.com).

CodePad makes it easier for C# developers to quickly test small code segments without having to create a full Visual Studio project. It's developed in C#.

The Open Source Macro Programming System (Implemented in C# atop the DLR)

Gives you the power of C++ at a cost of the simplicity of C#.

CSharpCompiler is a free and open-source library to compile c# source code programmatically. With extra features like error and warning handling. This library is so easy to use that you can create an IDE in minutes.

Notepad++ plugin for C# intellisense and CS-Script integration. Allows loading, executing and modifying C# scripts similar to the Visual Studio C# project.

Dazzer is an free & open-source 3D model studio for windows (and linux with WineHQ). Dazzer aims to create an complete standalone clone of blender.

This is a debugger visualizer add-on for Microsoft Visual Studio 2005. It gives you a quick way to run a SQL statement against a database connection and view the results in a grid while debugging your code.

Developer is a windows IDE that makes it easy to program in any language. It is developed in C#. It will support extensions and have a extensive API. It will also be social, connecting with popular websites and integrate with Facebook. It will also support all languages.

Fireball Framework is project that aim to create the best controls and libraries for developer, the project already contains some control, CodeEditorControl with Syntax Highlight, Collections,Outlook Navigation bar and etc..

A free deployment tool to create installer program for any .NET based applications but also dynamic updates from a web server. You can also publish directly your software to a web server with only a few clicks. It's mainly developed in C# but contains portions in C++.

Ela is a modern functional programming language that runs on CLR and Mono. It provides an extensive support for the functional programming paradigm.