MockFlow is an online tool for creating wireframes of software and websites. It helps to enhance your planning process by enabling to quickly design and share interactive UI mockups. It also comes with ready-to-use 70+ Components and 200+ icons, all designed to suit wireframing.

Nothing to download or install, create and access your mockups from anywhere. You can share your mockups in private/public mode and get feedback from your clients & users, As simple as sharing an URL. The Basic account is completely free with 10 MB storage.

twitter-mockup

Requirements: -
Demo: http://mockflow.com/
License: License Free