A GitHub Pages site for running the official ECMAScript conformance tests, test262, in a browser - here.
Prior to this, it hadn't been possible to run an up-to-date version of test262 in a long time. There's still old versions of the website floating around, e.g. here; this is intended to replace them. It's several times faster and allows you to provide your own copy of the tests, so as to not get out of date and to support development.
You can either provide a local .zip of the repo (with or without .git/), or click 'Remote' to load the one hosted in this repository.
The hosted copy was last updated on 05 November, 2018.
A version allowing preprocessing of tests, intended for tool authors, is available here.