CoBuild At Home : virtual maker activities
The Community Science Workshop Network : STEM-rich activities and projects,
admittedly, a little juvenile for high school, but great for review!
Exploratorium : science experiments and activites presented by the preeminent science museum in San Francisco.
Science Friday : a library of maker challenge projects
Make Code : virtual coding and app development for students
Scratch : the Scratch programming language and library of activities
Algodoo : Algodoo is an app which allows users to create physics simulation