Tools

Interaction design starts on paper - Create beautiful UI through better wireframes.
UI Sketching – How to Make It Right and Why You Should Do This in All Projects - UI Sketching is, of course, kind of drawing on a paper… but it is not a usual drawing – its purpose is to reveal the result of problem-solving thinking.

Sketch - Sketch is a design toolkit built to help you create your best work — from your earliest ideas, through to final artwork. Mac only
Figma - Figma is the first interface design tool based in the browser, making it easier for teams to create software.
Marvel - Simple design, prototyping and collaboration.
UXPin - The Full-Stack UX Design Platform
Webflow - Gives designers and developers the power to design, build, and launch responsive websites visually, while writing clean, semantic code for you.
MockFlow - Super-easy wireframing and UX suite for designers.
Framer - Design everything from detailed icons to high-fidelity interactions—all in one place.
Atomic - Advanced interactive design features like logic, data, and variables, into the hands of every designer.
Affinity Designer - Professional graphic design software for desktop and iPad.
Pencil - An open-source GUI prototyping tool that's available for ALL platforms.
Visily - Simple wireframing and mockup tool powered by AI and built for non-designers.

Modular Scale - Tool to help web designers size their type in a more meaningful way.
Layoutit Grid - Quickly design web layouts, and get HTML and CSS code. Learn CSS Grid visually and build web layouts with our interactive CSS Grid Generator.
WebAIM Color Contrast Checker - Enter a foreground and background color in RGB hexadecimal format or choose a color using the color picker.

POP. Prototyping on paper - POP helps you transform your pen and paper ideas into an interactive iPhone or Android prototype.
UserTesting - User Experience Research Platform.
Loop11 - Informed design decisions built from numbers & stories.

Testing with Xcode - UI testing gives you the ability to find and interact with the UI of your app in order to validate the properties and state of the UI elements.

HTML, from MDN - To build websites, you should know about HTML — the fundamental technology used to define the structure of a webpage.
HTML Reference - Free guide to HTML. It features all elements and attributes.
HTML Fundamentals - SoloLearn interactive HTML tutorial is comprised of carefully selected content, quizzes, and checkpoints to ensure that you learn as much as possible, while also having as much fun as possible.
Learn to Code HTML & CSS - Outlining the fundamentals, this guide works through all common elements of front-end design and development.
The Best HTML and HTML5 Tutorials - HyperText Markup Language (HTML) is a markup language used to construct online documents and is the foundation of most websites today.

CSS, from MDN - While HTML is used to define the structure and semantics of your content, CSS is used to style it and lay it out.
CSS Reference - Free visual guide to CSS. It features the most popular properties, and explains them with illustrated and animated examples.
Marksheet - CSS Basics - For developers eager to learn how CSS can define the style and layout of a webpage.
CSS Grid Guide - The CoffeeCup Guide to liberating layout through CSS Grid.
CSS Cheat Sheet - Reference for CSS goodness.

JavaScript, from MDN - Prototype-based, multi-paradigm, dynamic language, supporting object-oriented, imperative, and declarative (e.g. functional programming) styles. Learn how to program in JavaScript with guides and tutorials.
Bestof.JS - Check out the most popular open-source projects and the latest trends about the web platform and node.js.
FreeCodeCamp - Learn to code for free.

Pure.css - Set of small, responsive CSS modules that you can use in every web project.
Milligram - Minimalist CSS framework.
Bulma - Modern CSS framework based on Flexbox.
Basscss - Lightning Fast Modular CSS with No Side Effects.
Skeleton - Dead simple, responsive boilerplate.
Lit - World's smallest responsive css framework.
Tailwind CSS - A Utility-First CSS Framework for Rapid UI Development.
Picnic CSS - Lightweight and beautiful library.
Animate.css - Just-add-water CSS animations.
Chota - A micro (~3kb) CSS framework.

Vue.js - The Progressive JavaScript Framework
React - JavaScript library for building user interfaces
Angular - One framework. Mobile & desktop.
Moment.js - Parse, validate, manipulate, and display dates and times in JavaScript.
Reef - A lightweight library for creating reactive, state-based components and UI.

Semantic UI - User Interface is the language of the web.
UIkit - Lightweight and modular front-end framework for developing fast and powerful web interfaces.
Bootstrap - Build responsive, mobile-first projects on the web with the world's most popular front-end component library.
Foundation - The most advanced responsive front-end framework in the world.
Materialize - Modern responsive CSS framework based on Material Design by Google.
Metro UI CSS - The front-end framework for developing projects on the web in Windows Metro Style
Fluent UI - A collection of UX frameworks for creating beautiful, cross-platform apps that share code, design, and interaction behavior.
HTML5 Boilerplate - The web’s most popular front-end template
Material-UI - An open-source React component library that implements Google's Material Design.
Framework7 - Full featured HTML framework for building iOS & Android apps.
Element - Vue 2.0 based component library for developers, designers and product managers.
Shoelace - Back to the basics CSS starter kit. For when you don’t need the whole boot.
AT UIKIT - Lightweight and Modular Front-End UI Library.
Vuesax - Frontend Vue components.
Onsen - The most beautiful and efficient way to develop HTML5 hybrid and mobile web apps.
Kelp - A UI library for people who love HTML, powered by modern CSS and Web Components.

Fffuel - A collection of color tools and free SVG generators for gradients, patterns, textures, shapes & backgrounds.

Storybook - The UI Development Environment You'll ♥️ to use.
React Styleguidist - Isolated React component development environment with a living style guide.
VUEDS - An open source tool for building Design Systems with Vue.js.
Fractal - Powerful component libraries & styleguides that fit the way you work.