ES6Katas.org is a simple website that lists various katas (small tasks) for learning ECMAScript 6 by doing it. Each kata links to tddbin and loads the according source code in there. All you have to do is fix the failing tests. And by doing so you are supposed to use and learn ES6 one small task and feature at a time.
While learning it I realized that writing unit tests is always a good way to learn new things, even language features. So that's how the first #es6kata came about. And since the new writing it down is a commit it all ended up in the katas repo and @basecode then brought up the idea to use a github search and make a site that lists all the katas. In the beginning I was sceptical, since I wasn't sure if it would really continue. But meanwhile there are already a good number of katas. That's how this repo came about.
This site uses react.js for abstracting away the DOM (as I like to call it). On top it also uses react.js for server-side rendering, which creates a static version of the page that loads in an instant and the client-side waiting times are minimal.