Kiwix is a free open app that lets you view Wikipedia, Project Gutenberg, StackExchange etc offline.
It's intended for people who cannot access a reliable internet connection, either for geographical or political reasons.
You can find out more here:
You can follow it on the Fediverse here:
It's available for Windows, Mac, Linux, Android, iOS, Firefox and Chrome.
mastodon.at is a microblogging site that federates with most instances on the Fediverse.