These are free or low-cost resources to help you learn more

Online Courses & Syllabi

Coursera - Large offering of courses from top universities around the world. Certificates and to take courses for a grade are generally low-cost, but content and materials for all courses on Coursera are available for free. Coursera also bundles courses into specializations around certain topics. Available in several languages.
MIT Open Courseware - Large collection of free MIT courses online. Syllabi are available online with textbooks and materials used in that course.
Khan Academy - Online learning courses from primary subjects to specializations through partnerships with NASA, MoMa, and MIT. Courses are free and feature practice exercises, videos, and a personalized learning dashboard.
edX - Massive Online Open Course (MOOC) platform from Harvard and MIT. Large consortium of university partners. Free with option for paid certificate. Available in several languages.
Stanford Online - Online courses offered across several Stanford schools and departments. Free courses and paid options.
StraighterLine - Monthly subscription service that allows learners to take courses online for college credits. Credits are transferrable to a network of over 100 universities.
Udemy - Learning marketplace with over 40,000 courses. Regular promotions lead to courses and bundles of courses for as little as $19.

Other favorite resources? Please comment below!