There is an app that can do screenshots in MacOSX Lion, what's the name? There is an app that can do screenshots in MacOSX Lion, what's the name? 

It comes from the OS, not a 3rd party app.
The built-in application is called Grab. You can find it under the Utilities folder in Applications.
You can also use keyboard shortcuts to take screen shots. Here's a quick guide from Apple:

In Mac OS X, you can use simple keyboard shortcuts to do all sorts of things, including capturing images of what’s on your Mac screen. For example, you can take a screen shot of your entire screen by holding down the Command and Shift keys and pressing a 3.
If you hold down the Command and Shift keys and press 4, Mac OS X turns the cursor into crosshairs you can use to select whatever portion of your display you’d like to capture in a screen shot.
If you immediately hit the Spacebar after typing Command-Shift-4, Mac OS X replaces those crosshairs with a little camera. Using the camera, you can take a screen shot of the Dock, the entire menu bar, a single open menu, the desktop, or any open window.