Opera Dragonfly 2008 – 2013
Opera's developer tools, built into the browser from Opera 9.5 in 2008. Dragonfly was itself a web application, written in HTML, CSS and JavaScript, and could debug Opera running on another device.
Everything in one window
Dragonfly brought together the tools web developers needed: a DOM inspector with live editing, a CSS inspector showing the cascade, a JavaScript debugger with breakpoints, a network monitor, a resource viewer, a storage inspector and an error console.
Its most unusual feature was remote debugging. Because Opera ran on phones, TVs and game consoles, Dragonfly could connect to Opera Mobile or to a TV across the network and inspect the page there, from the comfort of the desktop.
The code of Dragonfly was published under an open-source license, and new versions were pushed to users from Opera's servers without waiting for a browser update.
Screenshots
The DOM inspector.
The CSS inspector.
The JavaScript debugger.
The console.
Remote debugging of Opera Mobile.
The color picker.
The console overlay.