Internet contains free knowledge.
Internet Archives is one such site. Some of the free pdf articles in the site includes: How to be creative?, How to become the best in the world?, 100 Ways to Kill a Concept: Why Most Ideas Get Shot Down
CustomGuide has released some Quick Reference Guides for Microsoft, Mac and Adobe products. These printable quick references are free to use, distribute, and share!
MIT OpenCourseWare | MIT OpenCourseWare contains free and open educational resource (OER) for educators, students, and self-learners around the world.