List of free web-development stuff for developerππ½
If you're looking for all programming tools around web-development (not just free). Check this page List of web-development Programming Tools
Responsively
A must-have DevTool for all Front-End developers that will make your job easier.
Tag: devtools, web-development, productivity, responsive, browser
Mirrored User-interactions across all devices. Customizable preview layout to suit all your needs. One handy elements inspector for all devices in preview. 30+ built-in device profiles with option to add custom devices. One-click screenshot all your devices. Hot reloading supported for developers.

Trinket
Share Code from any Device. Trinket lets you run and write code in any browser, on any device.
Tag: course-builder, teaching, playground, web-development
Unlimited Basic Trinkets Python, HTML, GlowScript, Blocks and more Quick, Simple Sharing Remixing Customizable Code Editor Downloadable Code Free Activities Custom Courses

Firefox Developer Edition
Firefox Developer Edition is a version of Firefox that's tailored for web developers.
Tag: browser, web-development