Why can't I freaking buy plain old Meccano anymore? I can't get that thing out of my mind from the childhood days. I had one beautiful meccano set some 35+ years ago. I don't care about these Reactor pre-made BS boxes.
https://www.amazon.com/Meccano-Junior-100-Piece-Bucket/dp/B0...
https://www.amazon.com/Meccano-20070926-Junior-Bucket-150-Pi...
https://www.amazon.com/Erector-Advanced-Toolbox-Construction...
https://www.amazon.com/Meccano-6024795-Meccano-Erector-Advan...
(Results of a quick Amazon search. I'm sure there are more.)