A great responsive design tool for web designers and web developers, Duo. Nowadays everyone is making with responsive design, Duo is a fresh new web browser special designed for web development use with 2 views at the same time, mobile device and desktop views.
Duo is a premium product by Electric Pulp. Download it from Mac App Store and increase your development performance today! With Duo you may have great design experience through multiple screen in one rather than separately always.
Hope it’s a helpful tool to you! Happy sharing~
Cost: USD 4.99
Source: Read more about Duo