Growl is a free notification system for Mac OS X. It is extremely customizable and it is compatible with many different freewares and sharewares. It incorporates very well with Mac OS X and there are many different display styles. I find it very useful because FTP transfers take a while and I always do other stuff while it is copying. With Growl, as soon as it is done, I get a notification. A kind of notification that I can't stand is an icon bouncing in the Dock. The problem with the bouncing icon is that it interrupts my workflow, because I have to switch back to this application to stop it from bouncing. The Growl notifications disappears after a few seconds so I don't have to take care of it right away, but at least I know about it instantly. I find it is mostly useful with chat and FTP applications. I use it with Adium, Chax, ForkLift, Handbrake, Skype and Transmit. Once you start paying attention to the list of application that use Growl, you'll find a lot. You can download Growl here from MacUpdate.