DOMtastic is a small, fast, and modular DOM & Event library for modern browsers. Same familiar API as jQuery.
Works great stand-alone or paired up with e.g. Backbone or Angular.
Quill is a modern rich text editor built for compatibility and extensibility. It's a free, open source WYSIWYG editor built for the modern web.
howler.js is an audio library for the modern web. It defaults to Web Audio API and falls back to HTML5 Audio.