PBS Learning Media provides videos and activities in every discipline imaginable from preschool to high school. If you want to learn about it, you can probably find a resource for it here!
Khan Academy has free courses across the spectrum of K-12 education. They also offer daily schedules for kids age 4-18 to help them maintain their educational skills.
This Youtube channel has tons of playlists of fun videos on all sorts of subjects, from study skills to film studies. Created by young adult author John Green and his brother Hank. Don't forget to be awesome!
Big History Project weaves insights from many disciplines to form a single story that helps us better understand people, civilizations, and how we are connected to everything around us.
DPLA is a collection of public domain and open licensed materials. From ebooks to online museum exhibitions to sets of primary sources on every topic imaginable, this is a fascinating place to learn!
Duolingo is a fun way to learn a language! With 35 languages available for English speakers (everything from French to Klingon), this website and app has you work through simple lessons to develop your language proficiency.