Growl is getting a brand new update and it would be available through the Mac App Store.
The developer spoke about this new version:
There are a lot of great changes coming, including the improved apps tab, a new rollup tab, and a whole lot more. 1.4 also has a lot of fixes in it.
– Applications Tab Redesign! This is a major overhaul, and should be much easier to use.
– Moved Rollup controls to separate tab.
– Major improvements to networking.
– New slider switch for on/off switches
– Added keyboard support to position picker.
– General Tab Relayout.
– Networking tab – Add support for subscription
– History Tab, contextual menu for history table to jump to the app/notification settings
– Rollup tab is the new home of controls related to the Rollup window.
– Adding a new display should not require a restart of Growl now.