Open source software

Text Editors

Multi-platform

• BlueFish - Bluefish is a powerful editor targeted towards programmers and webdesigners
• Komodo Edit - Komodo Edit is a fast, smart, free and open-source code editor.
• jEdit - jEdit is a mature programmer's text editor with hundreds (counting the time developing plugins) of person-years of development behind it.

Windows

• PSPad - Editor for developers for Microsoft Windows systems
• Notepad++ - free source code editor and Notepad replacement that supports several languages.

Mac

• TextWrangler - TextWrangler is the “little brother” to BBEdit, a leading professional HTML and text editor for the Macintosh.

Programming IDEs

Multi-platform

• NetBeans - Develop desktop, mobile and web applications with Java, PHP, C/C++ and more.
• Eclipse - multi-language software development environment comprising an integrated development environment (IDE) and an extensible plug-in system.

Application Design (UML etc.)

• ArgoUML - ArgoUML is the leading open source UML modeling tool and includes support for all standard UML 1.4 diagrams.
• StarUML

FTP tools

Multi-platform

• Filezilla
• Cyberduck

Image Manipulation

Multi-platform

• Gimp

Mac

• Seashore

Office

• Open Office
• OpenProj