Pros: Open source software alternative to Microsoft Office/Google Docs. You can create basic text documents, spreadsheets, slideshows, and so much more.
Cons: User interface is a little clunky in places.
Official Tutorials: https://wiki.documentfoundation.org/Main_Page (Click on "Release Notes" for the most recent version)
Donate: https://www.libreoffice.org/donate/
Contribute: https://www.libreoffice.org/community/get-involved/
Pros: Open source software with a clean user interface designed to help you focus. You can even choose a custom background. In my opinion it is best for creative writing/storytelling.
Cons: I haven't used this program enough to know its flaws. Feedback is appreciated.
Donate: https://gottcode.org/focuswriter/ (See "donate" menu on lower right side)