Web Browsing

Mozilla Firefox The premier free, open-source browser. Tabs, pop-up blocking, themes, and extensions. Considered by many to be the world's best browser.

Video Player, BitTorrent, Podcasting

Miro Beautiful interface. Plays any video type (much more than windows media player). Subscribe to video RSS, download, and watch all in one. Torrent support. Search and download from YouTube and others.

IM - Instant Messaging

Pidgin Connect to multiple IM accounts simultaneously in a single app, including: AOL IM, MSN, and Jabber.

E-mail

Mozilla Thunderbird Powerful spam filtering, solid interface, and all the features you need.

RSS

RSSOwl Solid cross-platform RSS client.

Peer-to-Peer Filesharing

Cabos A simple, easy to use filesharing program. Gnutella network.

Gnucleus A very good Gnutella search and download filesharing program.

Video Playback

Miro Beautiful interface. Plays any video type (much more than windows media player). Subscribe to video RSS, download, and watch all in one. Torrent support. Search and download from YouTube and others.

VLC Plays more video files than most players: Quicktime, AVI, DIVX, OGG, and more. Pretty good interface.

MPlayer Similar to VLC-- plays loads of video formats.

Media Player Classic Compact, but powerful media player. Plays anything under the sun. No install necessary.

DVD Ripping / Video Conversion

Media Coder Great tool for ripping CDs, DVDs, etc and converting between tons of video formats.

Word Processing / Office Suites

OpenOffice.org Big, full featured suite of tools for word processing and spreadsheets. Compatible with and a free replacement for Microsoft Word documents. Also supports OpenDocument Format.

AbiWord A word processor. Leaner and quicker than OpenOffice. Compatible with Microsoft Word documents and OpenDocument Format.

Podcasting

Juice Solid podcasting client.

DVD Ripping

Handbrake DVD to MPEG-4 ripper/converter.

Sound Recording

Audacity Simple sound recording tool.

Graphics / Photo Editing

GIMP Photo editing application that rivals Photoshop in features.

Paint.NET Graphics editor with a very nice interface.

Inkscape Vector graphics application.

FTP / SFTP

Filezilla Excellent FTP program.

IRC

X-Chat 2 IRC client.

Archiving

PeaZip Fantastic archiving utility to extract and pack archives of an extensive amount of formats. PeaZip also features password protecting archives, keyfile support, system integration, a lovely interface, and much more.

Note Taking

Freemind An innovative application for note taking and outlining. Takes time to get used to, but some people swear by it.

Jarnal Open Source note taking application written in Java

Keynote Open Source note taking application, very good.

Personal Finance

TurboCASH Simple, easy to use application for managing personal finances.

Quasar Easy to use Accounting package

Chat Clients

More Web Browsing

K-Meleon Fast, nice web browser.

Amaya Browser for Windows W3C developed web browser and editor for multiple platforms

Screensaver

Electric Sheep Immersive, trippy screensaver.

More Filesharing

Frostwire GNUTella client based on the Limewire codebase.

3D Graphics and Modeling

Blender Powerful 3D Modeling software.

Stars and Outer Space

Celestia Open-source 3D planetarium software. Akin to traveling through space (outer space).

Stellarium "Renders realistic skys in realtime." See what you would see if your city wasn't so light-polluted. Used in real planetariums.

Games

Marathon: Aleph One Engine for Bungie's free FPS series Marathon. Play online, solo play with rich original story, many total conversions and thousands of maps.

Zombies 3D zombie strategy game.

Armagetron Advanced 3D Tron game.

BZFlag First-person tank game.

Battle for Wesnoth Fantasy / Strategy Game

Free File Hosting

CC Publisher Host Creative Commons video or audio files for free on archive.org with this easy uploader.

Security Tools

NMap Easy to use port scanner for Windows

Wireshark Network Protocol Analyzer, formerly called Ethereal

TrueCrypt Creates encrypted virtual hard drives for extra security

ClamWin Open Source Anti-Virus. Very good at detecting viruses. Can be plugged into hMailServer for e-mail protection LIMITATION: Real Time scanning not implemented yet

Eraser Delete files securely off your hard drive utilizing DoD standards

MP3 and Audio Tools

MP3 Gain Easy to use MP3 manipulation tool for Windows. adjusts sound levels on MP3's so they are all the same

MP3 Book Helper This program provides rapid Mp3 (ID3v1, ID3v2) and Ogg/Speex/Flac Vorbis tags editing and file renaming functions. Mass Tag editing is done using special variables and Regular Expressions.

musikCube Open Source MP3 Player, ripper and organizer written using the .NET Framework

Utilities

Cobian Backup Backup software.

7-Zip File archiver.

Developer tools

XEmacs The classic, super customizable editor, for Windows.

KompoZer Easy to use, open source WYSIWYG html editor

SharpDevelop Open Source IDE for the .NET Framework. Utilizes the multiple programming languages and Windows forms

Notepad ++ Open Source programmers notepad for Windows