Lucidchart
Online diagram and flowchart software that supports Microsoft Visio import and can work on any operating system.
Serena Prototype Composer - the best agile application prototyping tool is now free! View the demo, take the product tour, or download it free today.
Serena Prototype Composer the best agile application prototyping tool is now free! View the demo, take the product tour, or download it free today.
prototyping wireframing wireframe
Online diagram and flowchart software that supports Microsoft Visio import and can work on any operating system.
Freemium
OmniGraffle can help you make eye-popping graphic documents—quickly—by providing powerful styling tools, keeping lines connected to shapes even when they’re moved, and magically organizing diagrams with just one click.
Commercial Mac OS X iPad
Using Balsamiq Mockups feels like you are drawing, but its digital, so you can tweak and rearrange controls easily, and the end result is much cleaner.
Commercial Mac OS X Windows Web
Free web and mobile mockup tool. Transform your design and mockups into clickable interactive applications. Perfect way to validate ideas faster with lean startup thinking. Best tool for quick prototyping.
Freemium Web
Visio Viewer opens Visio drawings directly on a computer without conversion on external Web Servers. Viewing Visio documents is as simple as drag and dropping of files (with a .vsd, .vsdx, .vdx extension) to the Application window.
Commercial
mockingbird is an online tool that makes it easy for you to create, link together, preview, and share mockups of your website or application. It is not Flash based.
Commercial Web