I want to download and read the documentation offline. Is there a pdf of something?
I don’t know is there an official way to do this but you can use http://devdocs.io. There is an option to keep docs offline. Not so long ago they added support for Crystal lang.
If you use OSX, you can use the Dash app.
A bit late to the party, but you can fork the project and run
crystal doc from the root folder. That will build Crystal’s docs (the same you can find online at: https://crystal-lang.org/docs/) and put them under /doc