Except for professional education courses, edX courses are free for everyone. Some courses have a fee for verified certificates but are free to audit.

Offers more than 1,000 free online courses.

MIT OpenCourseWare (OCW) is a web-based publication of virtually all MIT course content. OCW is open and available to the world; materials have an Attribution-NonCommercial-ShareAlike Creative Commons license. OCW does not offer certificates of completion.

Provides free and open access to a selection of introductory courses taught by Yale instructors. No course credit, degree, or certificate is available through the Open Yale Courses website.

This site aggregates Massive Open Online Courses (MOOCs) from more than 470 different universities, including Stanford, Harvard, and the Massachusetts Institute of Technology (MIT). It also offers a notification/reminder service called MOOC Tracker.

A selection of open courses on a variety of subjects.

Offers more than 300 free, self-paced courses. All required course resources—including textbooks, videos, webpages, and activities—are accessible at no charge. Saylor courses also contain a free final exam with the opportunity to earn a free course completion certificate.

All Udacity courses offer free access to course materials, but some courses charge for the full course experience (including access to projects, code-review and feedback, a personal Coach, and verified certificates). The price varies depending on the course.

Open educational courses (Primarily K-12) covering math, science, computer programming, history, art history, economics, and more

Short courses accessible to students in any branch of science or engineering.

The Open Learning Initiative (OLI) is a grant-funded group at Carnegie Mellon University, offering innovative online courses to anyone who wants to learn or teach.

UCI Open is an open education project launched by the University of California, Irvine, that supports the needs of learners and educators everywhere.

Provides a full curriculum of recorded lectures covering undergraduate chemistry plus selected graduate topics. From UCI Open