[feature request] Offline usage

[Thatoo]

Is your feature request related to a problem? Please describe.
How could one use all wonderful content of these plateform when they don't have access to Internet?

Describe the solution you'd like
Allow downloading the plateform as a webapp with all its content. Ideally a webapp that could sync the content to retrieve recent changes when the user could connect again to Internet.

Describe alternatives you've considered
For smartphone, but that require more work, create an app that could download/sync the content from the plateform the user choose by indicating its URL.