Free IDEs

Eclipse is a kind of universal tool platform - an open extensible IDE for anything and nothing in particular.

Aptana Studio 3
Based on Eclipse, it supports JavaScript, HTML, DOM and CSS with code-completion, outlining, JavaScript debugging, error and warning notifications and integrated documentation. Additional plugins allow support for Ruby on Rails, PHP, Python, Perl,[1] Adobe AIR, Apple iPhone and Nokia WRT (Web Runtime).

WideStudio is an integrated development environment(IDE) to build GUI applications for Linux / FreeBSD / SOLARIS / Windows95/98/ME,Windows NT,Win2K. Supports C/C++, Perl, Python, and Ruby programing languages.

GRASP (Graphical Representations of Algorithms, Structures, and Processes) is a full-featured development environment, created specifically to provide automatic generation of software visualizations for the purpose of improving the comprehensibility of the software. Over the past three years, a new version of GRASP has been developed based on pcGRASP and UNIX GRASP, which were written in C/C++. This new version, called jGRASP, is implemented in Java, and thus, runs on all platforms with a Java Virtual Machine. As with the previous versions, jGRASP supports Java, C, C++, Ada, and VHDL, and it can be configured to work with almost any compiler.

Xwpe is a programming environment for UNIX systems. The user interface mimics the Borland C and Pascal family of products for MS-DOS.

cEdit is a freeware opensource IDE (Integrated Development Enviroment) with support for unlimited languages.

Free for non-commercial use, feature syntax highlighting with support for HTML, XHTML, CSS, JavaScript, PHP, Ruby, and more. Works on various flavors of Windows.

HAPedit is an acronym for Html Asp Php editor; a text-mode editor useful for all developers of dynamic web pages.

The V IDE for GNU C++ and Java
V is a free, multiple platform C++ gui framework designed to make it the easiest way to write C++ GUI applications available. V is available for X Athena, X Motif/Lesstif, all Windows platforms, and now including OS/2.

Csound Editor
Csound Editor is an integrated development environment for Csound compilers.