Cacoo

Cacoo is a user friendly online drawing tool that allows you to create a variety of diagrams such as site map, flowchart, mind map, wire frame, UML diagram and network diagram. Cacoo can be used free of charge.

Serena Prototype Composer

Serena Prototype Composer helps you quickly and accurately simulate how an application will look and function without writing any code.

Pencil Project

Pencil is built for the purpose of providing a free and open-source GUI prototyping tool that people can easily install and use to create mockups in popular desktop platforms.

MockingBird

Mockingbird is an online tool that makes it easy for you to create, link together, preview, and share mockups of your website or application.

Lumzy

Lumzy is a quick prototyping and mockup tool for software designers and developers. As a mockup tool, you can use it to create a rough sketch of how the final website or application will look.

Dojo Toolkit

Dojo saves you time and scales with your development process, using web standards as its platform. It’s the toolkit experienced developers turn to for building high quality desktop and mobile web applications.

Mockflow

MockFlow WireframePro is a web-based tool to design and collaborate user interface blueprints for websites and apps. Its helps to visualize the website’s interface, navigation and structure in short time.

DENIM

DENIM is a system that helps web site designers in the early stages of design. DENIM supports sketching input, allows design at different refinement levels, and unifies the levels through zooming.

hotgloo

A better way to create wireframes and prototypes for web & mobile.

Webalys

A free User Interface Design tool for Web Designers.