SnappyApp

SnappyApp is a utility that enables you to take snapshots of anything from your desktop. You can capture a window of another running program, your entire desktop or just a small area of your screen.
The application lives on your Menu Bar from where you can access your screenshot library (contains the snapshots you took with the app) and the Preferences panel.

You can define a global hotkey for immediately capturing your screen, use the built-in editing options to add text content to the resulting screenshot, and print snapshots directly from the app's main menu.

Furthermore, this program provides you with a quick way to share your screenshots directly from its main menu. You can share snapshots via Facebook, Twitter, Evernote or Pinterest account.

Unfortunately, SnappyApp comes with two flaws: it occasionally runs slow, especially when exporting screenshots and the fact that it supports only one output format for exporting snapshots (JPG).

Still, this program is free of charge. So, you have nothing to lose if you decide to give it a shot on your Mac.