Build Rapidly WebSite Screens with Balsamiq Mockup

Balsamiq makes desigining of mockup screens for the website and phone quicker and easier with its drag and drop a library of common design elements around a work space, then export their final product in PNG or into a Confluence wiki, xwiki, JIRA and FogBugz.
 Using Mockups feels like drawing, but because it’s digital, you can tweak and rearrange easily. Teams can come up with a design and iterate over it in real-time in the course of a meeting.

Product managers, designers, developers, and even clients can now work together in the same tool to quickly iterate over wireframes, before writing code

Quick Add for Speed
Lets you build wireframes using your keyboard

Drag and Drop for Simplicity
Interfaces with drag and drop components–anyone can use it

Re-usable Symbol Libraries
Create templates, masters, and re-usable component libraries

Full Keyboard Support
CTRL+C, V, X, Z all you want!

Import and Export
Seamless integration with all versions of Mockups, for when you’re back online

Works Offline
Work on the plane or in a coffeeshop without an Internet connection

Mac, Windows, and Linux
Fully cross-platform

Low-Fi Sketch Wireframes
Sketchy, low-fidelity wireframes let you focus design conversations on functionality

UI Components & Icons
75 built-in user interface components and 187 icons, plus a whole lot of community-generated components.

Click-Through Prototypes
Linking lets you generate click-through prototypes for demos & usability testing

Export to PNG or PDF
Share or present mockups with embedded links using PDF export, or use a 3rd party tool to export to code.

It is a mockup creation tool built on Adobe AIR, you can try web demo here