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Life & fun · December 12, 2013

Duo

Dual-paned web browser for responsive web design.

Duo launched on December 12, 2013 with 72 votes, #235 of 927 launches that month. The site was still online in September 2026, 12 years on.

Visit apps.apple.com ↗Duo alternativestop 25% of December 2013

In plain words

Duo is a dual-paned web browser designed for developers and QA professionals who need to preview responsive web design layouts. The application displays two browser windows side-by-side, allowing users to view how websites appear at different screen sizes simultaneously. It features a straightforward interface and supports user agent customization. While not intended to replace comprehensive testing platforms, Duo serves as a quick screening tool during the development phase before running tests on dedicated testing services.

written from the facts on this page · October 2026

From the sources

Download Duo by Electric Pulp on the App Store. See screenshots, ratings and reviews, user tips, and more apps like Duo.

I love the simple user interface. And this really helps when previewing fully responsive sites; but if also let you set the user agent … that would make it complete, to me. I love the simple user interface. And this really helps when previewing fully responsive sites; but if also let you set the user agent … that would make it complete, to me. I build and do QA on a lot of web sites and I love this thing. It’s not a replacement for a real testing tool like BrowserStack or Sauce Labs, but it’s a great screening tool for use during development before you run tests on real testing tools like that.I was a little nervous when I bought it that it hasn’t been updated in a while, but it works fine…from apps.apple.com

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