https://devdocs.io/ https://devdocs.io/ exposes a huge catalog of indexed and searchable collections of documentation for a wide variety of languages, libraries

https://devdocs.io/ https://devdocs.io/ exposes a huge catalog of indexed and searchable collections of documentation for a wide variety of languages, libraries, and subjects, including HTML, JS, and CSS – though, the only GL I see is WebGL – and _all_ of it can be downloaded to an IndexedDB for offline use. It's been a very handy tool in my toolbelt.