Dev-PHP is a well-featured integrated development environment (IDE). You'll be able to create scripts and applications using the PHP scripting language and the PHP-GTK library (both included in the "PHP Package").
Dev-PHP is free software under the GNU General Public License, which means you can freely modify or use the source code under the terms of the license.

Home page for Python, an interpreted, interactive, object-oriented, extensible programming language. It provides an extraordinary combination of clarity and versatility, and is free and comprehensively ported.

Python for Windows extensions.

PythonCard is a GUI construction kit for building cross-platform desktop applications on Windows, Mac OS X, and Linux, using the Python language.

Ruby :: a dynamic, open source programming language with a focus on simplicity and productivity. It has an elegant syntax that is natural to read and easy to write.

PLT Scheme is an umbrella name for a family of implementations of the Scheme programming language.

MayaVi is a free, easy to use scientific data visualizer. It is written in Python and uses the amazing Visualization Toolkit (VTK) for the graphics. It provides a GUI written using Tkinter. MayaVi is free and distributed under the conditions of the BSD license. It is also cross platform and should run on any platform where both Python and VTK are available (which is almost any *nix, Mac OSX or Windows).

Prima is an extensible Perl toolkit for multi-platform GUI development. Platforms supported include Linux, Windows NT/9x/2K, OS/2 and UNIX/X11 workstations (FreeBSD, IRIX, SunOS, Solaris and others).

The toolkit contains a rich set of standard widgets and has emphasis on 2D image processing tasks. A Perl program using PRIMA looks and behaves identically on X, Win32 and OS/2 PM.

Code Browser is a folding and outlining editor for Linux and Windows.

The editor is between a traditional text editor, a smalltalk class browser and a web browser like mozilla. It displays a structured text file (marker-based folding) hierarchically using multiple panes.

It is especially designed to keep a good overview of the code of large projects. Ideal if you are fed up of having to scroll through thousands of lines of code.