Offline API documentation sets

macOS       https://kapeli.com/dash       
Dash gives your Mac instant offline access to 150+ API documentation setscumen


Windows     http://velocity.silverlakesoftware.com/
Velocity gives your Windows desktop offline access to over 150 API documentation sets


Linux       https://zealdocs.org/
An offline documentation browser inspired by Dash,Available for Linux and Windows.

Offline MDN Docs

https://kapeli.com/mdn_offline