https://www.colmanweb.co.uk/problemsolving/ukmt.htm
https://mindyourdecisions.com/blog/
https://www.transum.org/
https://www.resourceaholic.com/
https://mrrowe.com/about/
https://brilliant.org/daily-problems/
https://ssddproblems.com/
https://www.mathspad.co.uk/
https://undergroundmathematics.org/
https://www.openmiddle.com/
https://puzzlesandfigures.blogspot.com/
https://www.goteachmaths.co.uk/
https://phet.colorado.edu/en/simulations/filter?subjects=math,motion&type=html&sort=alpha&view=grid
http://www.physicswithperrone.com/kinematics-6.html (Great explanations of physics and mathematics)
https://shiny.rit.albany.edu/stat/binomial/
https://mathigon.org/