Kiwix: Download All of Wikipedia for Offline Reading (83GB) & More Content Packages
Project site: https://www.kiwix.org/en/
Links to content for download (or I guess you're able to within the app?) https://wiki.kiwix.org/wiki/Content_in_all_languages
Explanation of labels on files: https://download.kiwix.org/zim/README
Overview of content they offer for download: all of wikipedia (without audio or video, 83GB), gutenberg's public domain works (40,000+, 65GB), 167 stackexchange forums, various wikimedia projects (related to wikipedia: wikisource, wikinews, wikivoyage, wikihow, wikiversity, wikiquotes), and some other random forums (ubuntu or appropedia come to mind as listed), and others
They also have TED talks and Khan Academy videos, but I don't see why you couldn't just use something like youtube-dl to download specific ones you want (and this reminds me that I guess you could probably freely download and share such videos online with creative commons licenses)