Growl is the open source notification system for Mac OS X. Growl comes in 20 themes pre-installed. Personally I use Growl for Firefox, Spotify, TweetDeck, etc. to show me when I have new notifications. When Apple’s Mountain Lion operating system is released, it will have Notification Center built-in, which competes directly against Growl. Growl has responded directly to Notification Center coming to the new operating system.
“Growl is alive and kicking – We are still actively working on shipping two future versions of Growl. Our understanding from press reports at this point is that Notification Center is only available to apps from the Mac App Store, which effectively locks out the entire class of applications that aren’t or can’t be in the store” said Growl in a statement. “We’re investigating options for integrating Growl with Notification Center. It’s pretty early on, but we expect to find some way to provide integration for both developers and users. We want the work that developers have to do to add notification support to their application running on 10.6-10.8 to be painless and seamless.”