Growl is a truly great application for being reminded about these things that you have to do. But its greatness ends the moment you stray away from your PC and are sitting in front of a Mac. They are not supported yet, and by the looks of it they are not going to be supported anytime soon. But there is no reason to worry as long as an application like Notificant is around.
Available at the Mac App Store for a fiver, this new tool lets you send notifications to all the Macs that you have in your home and/or office, from just wherever you are. So, if you are using a PC and you know that later on you will be on your MacBook Air then sending yourself a reminder to do something will be as easy as pie. Or as easy as using Growl, at the very least.
The way these notifications are served, now, is really practical. They are not intrusive at all – they float on top of windows, and they are vanished the moment you click on them. You can also choose to have sounds associated with them, and even complete silence. And notifications can also be sent to your email address if that is what you want.
Notificant.com In Their Own Words
Notificant is a nifty little app that makes sure you always remember what you want to.
Why Notificant.com It Might Be A Killer
It does for Macs what Growl does for PCs. And it is really cheap, too.
Some Questions About Notificant.com
Is there a thing or two that Growl could learn from Notificant? 
