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Not really a client...

There is no ftp application in Jaguar, it is part of the OS. Of course you can connect from Terminal, but in the Finder type Apple-K and it will bring up the "Connect to Server" dialog box. Just type ftp://blah.blah.blah and it'll mount it like a hard drive after authenticating. Some ftp servers are a little sketchy with this method, so there are 3rd party solutions. Check around http://www.apple.com/macosx/downloads or http://www.download.com for some others.
 
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