Khan Academy - Khan Academy offers online tools to help students learn about a variety of important school subjects. Tools include videos, practice exercises, and materials for instructors. Read more about Khan Academy.
Calcohol - Need to dilute alcohol? How fast water start to boiling?
Brilliant.org - Brilliant - Understand concepts and build your problem solving skills with thousands of free problems and examples in math, science, and engineering.
HappyCoding - Simplify your iOS & macOS development.
Ixl - K-12 learning platform
Udemy - Online Courses - Learn Anything, On Your Schedule