Balsamiq Wireframes is a rapid low-fidelity UI wireframing tool that reproduces the experience of sketching on a notepad or whiteboard, but using a computer.
It really forces you to focus on structure and content, avoiding lengthy discussions about colors and details that should come later in the process.
Wireframes is FAST: you will generate more ideas, so you can throw out the bad ones and discover the best solutions.
Download Balsamiq Mockups 3.5.17 from its official website so you are always up to date with the new updates.
You can also download the keygen for all Balsamiq 100% virus-free products from Zippyshare.