- Awesome Electronics: https://github.com/kitspace/awesome-electronics
- Open-source Electrical Engineering Curriculum: https://github.com/Artoriuz/OSEE
- Rossmann Repair Training Guide (Louis Rossmann is autistic, btw): https://docs.google.com/presentation/d/1PkeO_lC5WTPScSV3ZzEEjVuDWeQtL2eHK6jEcf7axA0/htmlpresent
- Open Source Society University: https://github.com/ossu
- The Engineering Toolbox: https://www.engineeringtoolbox.com/
- HyperPhysics: http://hyperphysics.phy-astr.gsu.edu/hbase/hframe.html
- Awesome Math: https://github.com/rossant/awesome-math
- Learn Anything: https://github.com/learn-anything
- MIT OpenCourseWare: https://ocw.mit.edu/
- Free Harvard Online Courses: https://pll.harvard.edu/catalog/free
- Open Yale Courses: https://oyc.yale.edu/
- Library Genesis is your friend if you want to sail the seven seas for textbooks. I typically look up recommended books for different subjects from forum q&a's on the internet, including reddit and stackexchange, and then I set sail to the good ol' libgen.
- Archive.org for books and media as well
If you search online for awesome {insert subject here} git (or github), you will find many curated lists of resources. For example: Awesome Mechanical Engineering Resources and Awesome Biology