Open source software

Text Editors

Windows

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

Mac

• jEdit - jEdit is a mature programmer's text editor with hundreds (counting the time developing plugins) of person-years of development behind it.
• TextWrangler
• BlueFish
• Komodo Edit

Programming IDEs

• NetBeans
• Eclipse

Application Design (UML etc.)

• ArgoUML
• StarUML

FTP tools

Multi-platform

• Filezilla
• Cyberduck

Image Manipulation

Multi-platform

• Gimp

Mac

• Seashore

Office

• Open Office
• OpenProj