Kiwix is a free open source app that lets you view and search Wikipedia, other wikis and reference sites like StackExchange entirely offline. You can follow at:
The app is available for Android, iPhone, Linux, Mac and Windows from the official site at https://www.kiwix.org
It's also available via #FDroid
It's really useful if you are temporarily or permanently without a reliable internet connection.
This is a brand new server run by the main developers of the project as a spin-off of mastodon.social It is not focused on any particular niche interest - everyone is welcome as long as you follow our code of conduct!