a Windows application that allows you to look at the messages being sent in the system. When developing your own applications you can see the messages and you can inspect them
a free source code editor which supports several programming languages running under the MS Windows environment. based on Scintilla edit component (a very powerful editor component)
a free, open-source password manager or safe which helps you to manage your passwords in a secure way. You can put all your passwords in one database, which is locked with one master key or a key-disk. (there is also a freakish .net version)
Win32-versions of GNU tools, or tools with a similar open source licence. The ports are native ports, that is they rely only on libraries provided with any 32-bits MS-Windows operating system, such as MS-Windows 95 / 98 / 2000 / NT / XP