Create diagrams and drawings such as a flowchart, mind map, network diagram, UML diagram, wireframe, user interface design and other drawings online with free flowchart software.

Draw, share and collaborate on online diagrams. Easy web flow chart, network diagram, mockup, wireframe, UML diagrams like Class, Sequence, & data flow and process flow diagrams.

Fluid UI is the fastest browser-based mobile app prototyping tool available. Design and test your low and high fidelity app mockups on a mobile device with ease. Simple and UX oriented, this UI tool helps unlock creativity and will save your team time and money while gathering app requirements.

Web-based HotGloo is a rich internet application designed to create functional, interactive wireframes and is intended for use in web projects to help visualize planning processes, co-work with team members, coordinate website contents with clients and provide a precise framework for designers and coders.

Application design and prototyping solution. Quickly and effortlessly design, develop, prototype and document high-level User Interfaces of new and existing applications. Supports multiple Screen Resolutions and Devices. Export to PNG and Word.

The Visio equivalent for the mac

The real graphics gurus use Illustrator (and Photoshop).
The power lies in the Vector art to make prototype design for as small as 320x480 to huge monitors.

SimpleDiagrams is a desktop tool that helps you create simple diagrams quickly.

It’s important for designers to translate the ideas in their heads into a tangible form that stakeholders can relate to. Prior to writing any code, wireframes are a great way to quickly map out the functionality and flow of a website or application. This helps anticipate conflicts (“That's not what I had in mind") early in the process, at a point where they are painless to correct.

Official link: http://office.microsoft.com/en-in/powerpoint/

Both online and offline (Adobe Air) tool for building wireframes.

Create wireframes & mockups with Eclipse.

One of first tool available for wireframes.

Create Clickable Wireframes for Mobile and Web Apps: quick, easy and Free!

The wireframe software used by 60% of the Fortune 100. Beyond a mockup tool, design interactive prototypes for websites and applications quickly and easily.

Only available on the iPad. Has evolved from basic to a very feature rich tool.

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

ProtoShare allows development teams to create simple gray-box wireframes and evolve them to rich prototypes during the website and web app development process. Interactive wireframes, clickable comps, and live website views are just the tip of what your team can accomplish to elicit superior requirements and reduce rework.

Although a chart program, lovely charts with its intuitive drag-and-drop interface makes wireframing an easy task.

This is a Firefox add-on to do GUI prototyping and simple sketching

A flash-based wireframing tool.

Java based wireframing tool that works across Windows, Mac, and Linux.

Plugin for creating low-fidelity wireframes in Microsoft PowerPoint.

No need to learn a new tool: prototype cheaply and quickly for iPad, iPhone, Android, Windows Phone 7, Facebook and web using Apple Keynote, Microsoft PowerPoint or OpenOffice Impress.

InVision allows you to create stunningly realistic interactive wireframes and beautiful high-fidelity prototypes in a whole new way.

Adobe InDesign CS6 desktop publishing software gives you pixel-perfect control over design and typography so you can create elegant and engaging page layouts/Wireframes for print or digital media.

Go through this pdf if you know how to do wireframing using InDesign ~
http://www.peterpixel.nl/writings/wireframing-using-indesign/

Create quick wireframes for iPhone app in Keynote by using pre-drawn & reusable interface elements.

Every web redesign project we get comes with an essential strategy document. This strategy document is a tailored roadmap laying out specifics for a successful relaunch including wireframes to help visualize how new web templates will take shape.

Keeping new media aside, paper still works as a good wireframing tool. Though the new media have definitely helped easing the whole process. Try using the templates here: http://webdesignledger.com/freebies/10-free-printable-web-design-wireframing-templates
http://www.smashingmagazine.com/2010/03/29/free-printable-sketching-wireframing-and-note-taking-pdf-templates/
Creative Prototyping with paper ~ http://blog.tackmobile.com/article/interface-origami/

iRise takes your mobile and web applications beyond prototypes, wireframes and mockups, creating interactive simulations so you can test drive before code.

iPlotz allows you to rapidly create clickable, navigable mockups and wireframes for prototyping websites and software applications.

Create a project, add wireframe pages with design components and discuss your creations with others

Online App that will guide you and your team through UX Design process. Includes beautiful and easy to use wireframe/prototype editor, review tool, templates of personas, Business Model Canvas and more.

Easily create interactive iPhone and iPad app prototypes, app wireframes and app mockups with our App Sketchbooks and iOS GUI element Kits. Learn how yo...