Adium

Connect to multiple IM accounts simultaneously in a single app, including: AOL IM, MSN, and Jabber. Beautiful, themable interface.
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Mozilla Thunderbird

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

Run Windows programs on your Intel Mac at near native speed. Works on G4 / G5 Macs too, but much slower.
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Vidalia

This TOR frontend keeps you anonymous on the web using military-grade techniques. For use with Firefox see: TorButton.
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Bean

Very fast and easy to use word processor. Live word count, autosaving, more.
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NeoOffice

Built on OpenOffice.org. Big, full featured suite of tools for word processing and spreadsheets. Compatible with Microsoft Word documents and OpenDocument Format.
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AbiWord

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

Very good all-around ftp program.
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OneButton FTP

Simple, fast FTP, with a focus on "advanced queuing".
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Fugu

Not as polished as Cyberduck, but has a side by side interface showing your files and the remote files.
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Smultron

Text / html editor. Integrates with Cyberduck for editing websites.
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Nvu

Visual tool for making websites (WYSIWYG html editor), comparable to Dreamweaver.
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Colloquy

Great IRC client.
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Freemind

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

PDF viewer.
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