responsively-org/responsively-app ? reverse-engineered prompt

I'd like to build a desktop app for web developers to make testing responsive designs easier. The main feature should be a window that shows a single website rendered across multiple device screens simultaneously, like an iPhone, a Pixel, and an tablet, all side-by-side.

It should have a library of common device presets, but also let users create their own. The key thing is that all interactions must be synchronized. When I scroll, click a link, or type in one device view, it should happen on all the other device views in real time. Please also include a unified web inspector to debug elements across all frames, and a one-click button to screenshot the entire layout. It should be a standalone app for Mac, Windows, and Linux. Also, create a small companion browser extension to send the current tab's URL directly to the app.