Comprehensive knowledge

• Guide by TeamDev (RU) (HTML coding)
• Interactive learning by freeCodeCamp (Front-end / Full-stack)
• Interactive learning by The Odin Project (Full-stack)
• Front-end Handbook 2018 by FrontendMasters (Front-end / Full-stack)

HTML / CSS

• Front-end Handbook 2018 HTML & CSS learning chapter
• HTML5 Doctor - HTML references
• HTML Dog - HTML guides
• Pug - another HTML template engine, popular in NodeJS community

Flexbox:

• Guide by CSS Tricks
• Guide by Scotch.io

Methodologies:

• BEM site, BEM styleguide (essential)
• SMACSS
• OOCSS article on Smashing magazine, Guide
• ITCSS article, ITCSS slides
• Atomic Design article

Books:

• "CSS: The Definitive Guide" by Eric Meyer
• "CSS3: The Missing Manual" by David McFarland
• "CSS Secrets" by Lea Verou

Frameworks:

• Bootstrap
• Foundation
• Tailwind CSS

CSS processors

Sass

Articles:

• TheSassWay

Code styleguide:

• Idiomatic pre CSS

Tutorials, guides:

• PostCSS Deep Dive

PostCSS

• GitHub repo
• A searchable catalog of PostCSS plugins

Noticable plugins:

• CSSNext
• Autoprefixer

Emails

• Foundation for Emails

JavaScript

• Front-end Handbook 2018 JavaScript learning chapter

Books:

• Eloquent JavaScript

How browsers work

• Optimising the front end for the browser (RU transalation)

Linters

• Stylelint
• ESLint

React

• Front-end Handbook 2018 React learning chapter
• "Start Learning React" from egghead.io

Redux:

• "Getting Started with Redux" by Dan Abramov
• "Building React Applications with Idiomatic Redux" by Dan Abramov

Vue

• awesome-vue repository - A curated list of awesome things related to Vue.js

Build

• Webpack guide by SurviveJS

Git

• Pro Git
• "Learn Version Control with Git" by git-tower
• GitHowTo
• Git style guide

Fonts

• CSS Font Stack - default fonts availability on OSs
• Typekit - if you have an account and subscription, you can assemble fonts (event most of the paid ones) in kits to connect to your website

Design

• Front-end Handbook 2018 "Learn User Interface/Interaction Design" learning chapter

UI/UX

• What Is User Experience Design? Overview, Tools And Resources
• Usability Checklist

Accessibility

• Accessibility Guidelines
• WAVE web accessibility evaluation tool

Useful plugins and libraries

Common:

• lodash - utilities (Vanilla JS)

Sliders:

• Swiper (Vanilla JS / jQuery)
• Slick (jQuery)

Lightboxes:

• Magnific Popup (jQuery)

Text trim:

• Shave

Custom forms:

• jcf

Custom scrolls:

• SimpleBar
• Overlay Scrollbars

IP information (location, etc):

• freegeoip

Sprites:

• svg-sprite - svg
• spritesmith - png, jpeg, etc

Lazy loading (images):

• lozad.js

Regression/visual testing:

• gemini
• BackstopJS
• Galen

Intersection:

• IntersectionObserver API - can be used with polyfills (use instead of inview.js and waypoints if possible)

Polyfills:

• Polyfill.io

Interesting people

• (RU)"names" by web standarts