CSS Stats – web-based app that visualizes various stats about your CSS files.

purifycss – detects which CSS selectors your app is using and creates a file without unnecessary CSS

Email Lab – open-source starter kit for HTML emails that uses Grunt

Google Fonts Simple – open-source project to tag, organize and make it easier to browse Google Fonts

resizr – emulates different screen sizes of many popular devices

Libraries.io – helps you find new open-source libraries, modules and frameworks

First Aid git – searchable collection of the most frequently asked asked questions about Git

Epic Favicon Generator will create 20 different favicon sizes for your site, from 16x16px all the way up to 196x196px.

CSS Font Sizing explores and compares the various methods of declaring font sizes with CSS.

localFont is an web-based Vanilla JS tool that converts font family files into a ready to use solution for localStorage web font caching.

CSS Gradient Animator is, as the name suggests, a handy little tool for quickly generating CSS gradients.

UX Recipe is a checklist where you discover, choose and estimate your next UX project tools & techniques.

This Typography Cheatsheet, created by Type Wolf, is a comprehensive guide to smart quotes, dashes & other typographic characters.

Device Metrics is a handy resource from Google Design for checking the screen size, resolution, aspect ratio of many devices.

Web Font Load is a tool that will allow you to install, via the terminal, ALL of Google’s Web Fonts at once.

Google Design

ai2html – ai2html is an open-source script for Adobe Illustrator that converts your Illustrator documents into html and css.

HTML Arrows – clean and colorful place for all the html symbol codes we could never seem to remember

GitHub Cheat Sheet – A list of cool features of Git and GitHub.

 

Source: 25 Useful Free Tools & Apps For Web Designers from 2015