The CalTech Jet Propulsion Lab offers NASA Activities, including projects, toolkits, videos, and contests.
Tinkercad is a free web app for 3D design, electronics, and coding.
Scratch is the world's largest free coding community, hosted by the Massachusetts Institute of Technology.
Having trouble understanding a math problem? Try betterexplained.com or watch a techmath video.
The Goodwill Community Free Global program has thousands of free tutorials on essential skills covering everything from resume writing, to using excel, or even HTML coding.
Digitallearn.org has many short instruction videos on computer and internet basics, plus useful tutorials such as using Healthcare.gov or buying a plane ticket online.