- ES6 Katas - Small, byte-size exercises to discover most aspects of ES6 features by doing interactive, online exercises. Pretty awesome.
- Learn ES2015 - A great part of Babel's website that takes you through examples of all supported ES6+ features
- ES6-Features.org - Nice ES6 / ES5 comparisons of many ES6 language features
- ES6 Features - A single-page tour of code examples for just about every ES6 feature, by Luke Hoban
- ES6 In Depth - A great series of articles on Mozilla Developer Network (MDN); also available in French through great translation efforts.