This is honestly one of the most under-hyped pieces of software for the Mac. You almost never hear it mentioned, at least I don’t, yet it is one of my favorites. There is always some Mac user ready to tell you about Quicksilver or a myriad of other Mac apps, but I find Growl to be one of the most satisfying of the bunch.

In its simplest, it is basically a notification system for the applications that run on your computer. It interfaces with a lot of applications and displays messages in the corner of your screen, not unlike the AIM pop-up notifications, only a lot less annoying. There are a number of styles for you to choose from to customize what the notifications look like, and you can change how long they are visible.

I have Growl display messages for Adium, Transmit, Firefox, Twitterrific, and Last.fm. It shows the name of the artist and the song title when a new song comes on in iTunes. It tells me when downloads are done in Firefox. I get alerted when a transfer session is done in Transmit. When new tweets are downloaded they are displayed on the screen. And with Adium, it does just about all the same things AIM does. It lets you know when buddies sign in/out and when you get messaged. It does this all without being intrusive or disturbing what you are currently in the middle of. The messages show up on the screen and slowly fade after a few seconds unless you hover your mouse cursor on them in which case they stay until you move your mouse.

It even works when the application is minimized, hidden, or if you’re using Spaces and it’s in a different space than you are currently working in. The notification from Growl comes up no matter what you are doing or what Space you are working in. This saves you plenty of time and prevents you from having to switch back and forth while you’re waiting for your file transfer to finish. You can continue to work and not worry that you’ll forget about the transfer.

I highly suggest Growl as it has made it a lot easier to get things done. It has also made my switch over to Mac OS X that much more pleasant. It’s a subtle tool that has such a profound impact. Growl is available online for free, you can go to www.growl.info to get it.