GIMP

Photo editing application that rivals Photoshop in features.
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Handbrake

DVD to MPEG-4 ripper/converter.
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Media Coder

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

Simple sound recording tool.
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7-Zip

File archiver.
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Mozilla Thunderbird

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

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