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Mathematics

mathplayground.com

https://www.mathsisfun.com

https://www.youtube.com/c/3blue1brown

Multimedia

VividMaths https://www.youtube.com/channel/UCYxuKF7OMfJ9FwprYpS3xug 

Programming

https://repl.it/languages

Host your own repl.it https://github.com/replit/repl.it

3D Print

https://tiny-machines-3d.myshopify.com/products/creality-cr-10s-large-build-area-3d-printer

NASA Models

https://3dprint.com/141333/nasa-3d-printable-models-kits/

Legacy Microscope Drivers

http://www.oasisscientific.com/downloads.html

Paid to Play games:

https://www.twitch.tv

Computer Science

https://eater.net

https://www.youtube.com/c/beneater
http://www.righto.com/2015/12/reverse-engineering-arm1-ancestor-of.html

Arduino 

http://file.allitebooks.com/20170204/Arduino%20For%20Dummies.pdf

http://cmuems.com/resources/getting_started_with_arduino.pdf

http://www.multimedialab.be/doc/erg/2017-2018/Arduino_A_Quick-Start_Guide_2nd_Edition_The_Pragmatic_Programmers_2015.pdf

Photography

https://www.nikonsmallworld.com