I've long used the [OctoTree Chrome extension](https://chrome.google.com/webstore/detail/octotree/bkhaagjahfmjljalopjnoealnfndnagc) for browsing GitHub with a full tree view of the folders and files. Insight.io adds some full-fledged IDE features to this. Code navigation, find references to classes and methods, definition lookup, and more. ([Also see my other favorite Chrome extensions](http://brettterpstra.com/2017/07/14/web-excursions-for-july-14-2017-chrome-edition/))
