GENERAL:

codepen
jsfiddle
freecodecamp
mdn web docs
neocities web guide
stack overflow
w3schools
css tricks
svg editor
sadgrl guides
sadgrl webmaster links

JAVASCRIPT LIBRARIES:

LAYOUTS:
isotope
masonry
muuri
packery

ANIMATION:
three
anime

UI:
angular
react
vue

GALLERIES & CAROUSELS:
lightbox v2
lightGallery
glide
flickity

STATIC SITE GENERATORS:

generator directory
hugo
gatsby
jekyll
eleventy

QUICK TOOLS:

css grid generator
flex generator
HTML formatter
CSS formatter
HTML validator
CSS validator
find unclosed divs
css grid visual cheatsheet
flexbox visual cheatsheet
accessibility tools

CODE EDITORS:

brackets
notepad++
sublime text
visual studio code

CSS LIBRARIES & FRAMEWORKS:

animate
bootstrap
bulma
foundation
milligram
pure
tailwind
semantic ui
water

PREMADE LAYOUTS:

codesharing layouts
eggramen pages
fool lovers (jp)
neothemes
sadgrl layouts
teppy’s layouts
tooplate