What are some of the cool links you've been meaning to look at?

I was going through my google keep and I found a million links to cool stuff I saw on HN. What are some you've been saving up?

Here's a few from me:

Perl-like one-liners with Ruby: https://github.com/learnbyexample/Command-line-text-processing/blob/master/ruby_one_liners.md

Deep Learning with Pytorch in 60 mins: https://pytorch.org/tutorials/beginner/deep_learning_60min_blitz.html

Financial modeling site & API that shows DCF, WACC and other data for stocks: https://financialmodelingprep.com/financial-summary/GOOGL