Nicotine is also the name of a (
GPL'd)client for the
Soulseek P2P network, for
*nix operating systems.
Written in Python, it is an updating/rewriting of an older client, Pyslsk, which is now no longer being updated. While it is primarily designed for Gnu/Linux systems and uses GTK and PyGTK, many people have reported making it work successfully on OSX as well.
In my own experience Nicotine is a nicer client to use than the Windows version, having all the same functionality (friend list, instant messaging, queuing of full folders, share to friends only option) plus some additional functions that are not currently available on the windows client, such as blocking IP addresses by country.
I had some problems installing this at first, even from RPMs, as it seemed to have some circular dependency problems which took several attempts to resolve, but it was the first application I had tried to install as a linux newbie, and no-one else I've spoken to has had these problems, so YMMV.
The only real problem I've had with Nicotine is that it is very memory-intensive, and will often freeze up on an older machine when other applications are running, or when it has been left running for more than a few hours (particularly galling when you have something queued behind several hundred people, get to the front of the line, and then it freezes, sometimes forcing you back to the end of the queue). This can cause a major problem if you have to kill the app - sometimes when you restart it after a forced kill, it comes back having lost all your user data, including your queued files.
This data is all backed up in the config.old file, and supposedly all that needs doing is to delete the config file, reinstall the program and then rename config.old to config . While others have reported success with this method, in my experience it rarely works, and it becomes necessary laboriously to go through the config.old file and manually re-add the information. But at least the information is saved somewhere, unlike many other file-sharing programs.(Update 28th May 2004 since writing this a later version, 1.08rc1, has been released. After two weeks of using this, while it still freezes as much as ever, it doesn't seem to lose the data any more)
On the whole I cannot unambiguously recommend Nicotine, but given the fairly poor competition, in the field of *nix file-sharing programs it's the best of a bad bunch.
Nicotine can be downloaded from http://nicotine.thegraveyard.org