Balsamiq. Rapid, effective and fun wireframing software. | Balsamiq.
A wireframing and mock up tool with a high focus on usability. Quickly come up with mock ups and easily share them with clients
Prototypes, Specifications, and Diagrams in One Tool | Axure Software
The prototyping and specification software used by 87% of the Fortune 100. Beyond mockups, design interactive prototypes for business solutions, website