Implement DNS in a Weekend
I love all the series about writing your own X in 100 lines of code.
It gives you the understanding of technology and removes a lot of unnecessary details.The great examples of this are
'A from-scratch tour of Bitcoin in Python' 
https://karpathy.github.io/2021/06/21/blockchain/
and 'Let's build GPT: from scratch, in code, spelled out'
https://youtu.be/kCc8FmEb1nY
from Andrej KarpathyI wonder if anybody tried to collect all such projects together and built his own 'Internet in just 100 lines of code'