Input
Openstax
Library of Openly-licensed, Peer-reviewed educational material for higher education such as Economics to Calculus to Python Programming. In fact while attending community college I used openstax for both Calculus 2 and 3.
Libretexts
Massive collection of open textbooks. Especially if you are interested in STEM related fields like Engineering and Biology.
Merlot
Another open-licensed peer-reviewed library of resources with an emphasis on higher education and multimedia materials.
MIT OpenCourseWare
Complete course materials from almost every MIT course since 2002. You find find courses on the arts and theatre to aerospace and quantum mechanics.
OER Commons
Huge searchable hub with materials from kindergarten through higher education and workforce training.
Khan Academy
Can't forget about good ole' Khan Academy. K–12 and some college topics (especially math, science, test prep). They even have cirriculum up to linear algebra, multivariable calculus, and differential equation assistance as well!
freeCodeCamp
Comprehensive coding curriculum with certifications - completely free
Public Launch
Officially live! The product is now available worldwide.