Free wireframing online tool

Origami is a free tool for designing modern user interfaces.

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.

Online diagram/mockups design.

BLOKK font gives you a nice fill text for mock-ups and wireframing without the lorem ipsum. The new and better wireframing font.

Maqetta is an open source project that provides WYSIWYG visual authoring of HTML5 user interfaces. The Maqetta application itself is authored in HTML, and therefore runs in the browser without requiring additional plugins or downloads.

Wireframing, mockups and prototyping for websites and applications

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