Amazon Lumberyard is a free AAA game engine deeply integrated with AWS and Twitch – with full source.

OpenGL support library so you can just dive in and write OpenGL code

Simple JavaScript testing framework for browsers and node.js

Emacs keybindings for the Sublime Text editor.

AngularJS - HTML enhanced for web apps!

JavaScript library to make drawing animation on SVG

Material UI: Comprehensive React component library that implements Google's Material Design. Free forever.