Cypress : JavaScript End to End Testing Framework. Fast, easy and reliable testing for anything that runs in a browser.
Chrome Experiments : Google Chrome Experiments is an online showroom of web browser based experiments, interactive programs, and artistic projects.
LokiJS : A fast, in-memory document-oriented datastore for node.js, browser and cordova
WebTorrent : WebTorrent is a streaming torrent client for the web browser and the desktop.
WebTorrent is written completely in JavaScript – the language of the web...
TraceKit : Not all browsers support stack traces on error objects, but TraceKit squeezes out as much useful information as possible and normalizes it.
A JavaScript file you can insert into your pages to simulate the Firebug console in browsers that are not named Firefox.