Here are some popular new github repositories that can be interesting for web developers. All of them earned their first 1500 stars in 2016.
Dependency Management
Yarn — Fast, reliable, and secure dependency management. https://yarnpkg.com (Oct 2016)
React
React in patterns — List of design patterns/techniques used while developing with React (Jul 2016)
React Boilerplates
Create React App — Create React apps with no build configuration (Jul 2016)
Next.js — A minimalistic framework for universal server-rendered React applications https://zeit.co/blog/next (Oct 2016)
React Slingshot — React + Redux starter kit / boilerplate with Babel, hot reloading, testing, linting and a working example app, all built in (Jan 2016)
UI Components
Draft.js — A React framework for building text editors. https://facebook.github.io/draft-js/ (Mar 2016)
Recharts — Redefined chart library built with React and D3 http://recharts.org (Jan 2016)
Styled Components — Visual primitives for the component age 💅 http://styled-components.com (Sep 2016)
React-dates — An easily internationalizable, mobile-friendly datepicker library for the web http://airbnb.io/react-dates (Aug 2016)
End to end testing
TestCafe — Automated browser testing for the modern web development stack. https://devexpress.github.io/testcafe (Oct 2016)
Javascript frameworks
MJML — the only framework that makes responsive-email easy https://mjml.io (Feb 2016)
Choo — 🚂🚋🚋🚋 — sturdy frontend framework https://bit.ly/choo-handbook (May 2016)
Svelte — The magical disappearing UI framework https://svelte.technology (Nov 2016)
UI Widgets, plugins, components
Flatpickr — lightweight and powerful datetimepicker with no dependencies https://chmln.github.io/flatpickr (Apr 2016)
Algolia Places — 🌐 Turn any <input> into an address autocomplete https://community.algolia.com/places/ (Apr 2016)
Popper.js — A kickass library to manage your poppers https://popper.js.org (Apr 2016)
Bideo.js — Fullscreen HTML5 Background Video for the Web. https://rishabhp.github.io/bideo.js/ (May 2016)
Anime.js — Javascript Animation Engine http://anime-js.com (Jun 2016)
Utilites, tools
Parse Server — Parse-compatible API server module for Node/Express https://parse.com (Jan 2016)
Webpack-dashboard — A CLI dashboard for webpack dev server (Aug 2016)
Lighthouse — Auditing, performance metrics, and best practices for Progressive Web Apps (Mar 2016)
date-fns — ⏳ Modern JavaScript date utility library ⌛️ https://date-fns.org (Mar 2016)
Optimize-js — Optimize a JavaScript file for faster initial load by wrapping eagerly-invoked functions (Sep 2016)
vConsole — A lightweight, extendable front-end developer tool for mobile web page (Apr 2016)
Tutorials
JavaScript Stack from Scratch — Step-by-step tutorial to build a modern JavaScript stack from scratch
es6-cheatsheet — ES2015 [ES6] cheatsheet containing tips, tricks, best practices and code snippets
52 technologies in 2016 — Let’s learn a new technology every week. A new technology blog every Sunday in 2016
… and a couple more
These are repositories that emerged at the end of 2015 but became popular in 2016.
Inferno — An extremely fast, React-like JavaScript library for building modern user interfaces http://infernojs.org
Preact — Fast 3kb React alternative with the same ES6 API. Components & Virtual DOM. https://preactjs.com