Adium - IM client, works with multiple services
CamTwist: broadcast your desktop as a video source in skype, etc (though not iChat)
CocoThumbX: Great utility for creating thumbnail images of files including BMP, TIFF, GIF, PNG, JPG, PICT, PDF, EPS, DOC, RTF, RTFD, HTML, CSS, TXT and QuickTime supported Movies.
Cyberduck: FTP and SFTP client
EasyFind: Even faster than Spotlight
Flock browser: The social browser
Flip4Mac: Play WMA and WMV files in QuickTime Player--no need for Windows Media Player!
iSquint: Convert video files for iPod or other handhelds
Jing: Free screen capture (still image and video) for Mac & PC
Joost: Internet TV
KompoZer: A more recent spin-off of Netscape Composer, then Mozilla Composer, then Nvu, now KompoZer--very good built-in CSS editor for newbies
MacTracker: Know everything about your Macs (and all others)
MeBeam: No software to download, just enter a room name to video conference with multiple people for free!
Miro: Internet TV (and video podcasts, torrents, etc.)
Mousepose: OK, this one ain't free, but it's worth the price for highlighting areas of your screen for demos and screencasts!
NeoOffice: OpenOffice for Mac (free alternative to MS Office)
Paparazzi: Easily create screen captures of full web pages
SecondLife: Multi-User Virtual Environment (MUVE)
Skype: VoIP and video conferencing solution
ThumbsUp: Another great thumbnail maker for files
Thunderbird: Great alternative to OS Mail, a Mozilla project
Transmission: BitTorrent client
Jiggler: Jiggle the mouse at specified intervals to keep your Mac from sleeping
Onyx: Enable hidden features of OS X or run maintenance scripts.
SuperDuper: Backup utility software, create a bootable clone of your startup disk.
Vienna: Free RSS/Atom newsreader
VLC: Video player, plays multiple video formats
Web Minimalist: Great simple and free HTML editor with built-in preview--excellent for teaching HTML and web design
YemuZip: Great Zip compression utility, create Zip files in native PC or Mac formats
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