Free Applications for Microsoft Windows XP/Vista/7

Audio

Audacity A free closs platform digital audio editing application with multiple track capabilities.

File Sharing

Cabos A file sharing program for the Gnutella network based on LimeWire and Acquisition.
eMule An ED2K and Kad network file sharing application.

Graphics

Blender A free suite of 3D creational tools.
GIMP A free image editing application similar in functionality to Adobe's PhotoShop.
InkScape Inkscape is a Vector Graphics Editor, similar to Adobe Illustrator, that strives to be SVG Compliant, open source, responsive and extensible.
Paint.NET A free image editor with enhanced features including layers, unlimited undo, and special effects.

Internet

Juice Juice is a cross-platform media aggregator that automatically downloads files to your computer or portable device, leaving you one-click-away from latest media.
Miranda IM Miranda IM is an open-source multi protocol instant messenger client for Microsoft Windows. It's smaller, faster, and easier!
Mozilla Thunderbird Open source cross-platform email and Usenet client based on Mozilla code. Features intelligent spam filters, built-in RSS reader, and quick search.
Pidgin Pidgin is an easy to use and free chat client used by millions. Connect to AIM, MSN, Yahoo, and more chat networks all at once.
RSSOwl RSSOwl is a powerful application to organize, search and read all your news feeds in a comfortable way.

Multimedia

Last.FM Learn about your favorite artists, find nearby concerts, and share your music tastes with the Last.fm scrobbler.

Office

GNUCash GnuCash is a simple and free accounting software, similar to QuickBooks but more lightweight.
NotePad++ NotePad++ is a robust replacement for Windows' basic text editor, with a focus on code editing.
OpenOffice OpenOffice is the largest open source office suite, including applications for word processing, spreadsheets, and more!

Security

ClamWin An anti-virus program for Windows based on the popular ClamAV virus scanning library.
SpyBot - Search & Destroy SpyBot S&D is detects and removes spyware and adware from your computer. It can also clean usage tracks.
TrueCrypt TrueCrypt is free open-source disk encryption software for Windows 7/Vista/XP, Mac OS X and Linux.

Tools

7-Zip Open source Windows utility for manipulating archives. Formats 7z, ZIP, GZIP, BZIP2 and TAR are supported fully, other formats can be unpacked.
DropBox A file hosting service with easy synchronization and sharing features.
FileZilla A cross platform FTP and SFTP client with an easy to use graphical interface.
InfraRecorder A free CD and DVD burning solution with advanced features and Windows Explorer integration.
Synergy An innovative Windows application that allows you to share a single mouse and keyboard between multiple computers.
ZScreen A screen capturing program for Windows with many useful features.

Video

HandBrake HandBrake is an open-source, GPL-licensed, multiplatform, multithreaded video transcoder, available for MacOS X, Linux and Windows.
Miro Video Converter A super simple way to convert almost any video to MP4, Ogg Theora, or a specific phone or iPod.
VLC VLC media player is a highly portable multimedia player and multimedia framework capable of reading most audio and video formats as well as DVDs, Audio CDs VCDs, and various streaming protocols.

Web Browsers

Google Chrome Google Chrome is Google's browser software, designed with simplicity and ease of use in mind.
Mozilla Firefox The Mozilla Firefox web browser is the new fast, stable, and secure way to browse the internet!