Cut through the crap, when it comes to Mac OS X apps! I've spent time talking to friends, and testing out applications. These are my favorites. I don't post everything; on the contrary, I put up only the best of breed. You won't find any junk here, other than maybe my design.
Suggest a KILLER app.

File Sharing

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Azureus
One of the most featured multi-platform BitTorrent applications in existance, Azureus is the core application for the Vuze service. While it offers some advanced features such as encryption, anonymous transfering (Tor), and multi-platform support, it does
 
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Cyberduck
Quick, simple, and free FTP and SFTP client. The best part: includes Quicksilver and Growl support.
 
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SolarSeek
An easy to use application for finding music on the SoulSeek networks. If you are looking for specialized and hard-to-find material, this is the application you want to use.
 
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Transmission
A really easy to use BitTorrent client. There's nothing fancy about this utility, but it's quick and dirty.