Tary pop up notifications in OS x
===

I need to show something similar to skype pop up saying "A came online" in my OS x app. When I researched on this I found that we can use Growl for achieving it. But for this, do every user who use my app needs to install Growl too?

Is there any way I can make a standalone app for showing notifications? Because we are not installing Growl or any other softwares when installing skype, but still they are showing the notification pop up.

I am really confused. Please help me out! Thanks in advance!