Duo is a dual-paned web browser that lets you browse the web in two views: your standard ‘desktop’ view as well as a typical ‘mobile’ view. By seeing these two views at the same time, you’re able to quickly test and work through multiple screen experiences rather than considering them separately.

Whether you’re a designer or a developer, project manager or client, Duo gives you a new tool to make your Responsive Web Design project go more smoothly than ever.

Get the bookmarklet: http://helloduo.com

Features:

• Fixed mobile view: Duo gives you a typical ‘mobile’ view using a fixed-width pane.
• Tablet / desktop view: In your second pane, browse the web using any width you’d like.
• Synchronized browsing: Navigating in either pane updates the other. No need to reload layouts to view pages at different sizes.
• Webkit dev tools included: Duo has everything you need to make sure your design is doing what it should. Debug code in either pane.
• Convenient key commands: Duo includes tools for clearing your cache and getting rid of those pesky cookies via standard key commands.
• Handy bookmarklet: Use the convenient bookmarklet in your other browsers to push a site over to Duo.