This looks like a really nice, visual, first intro to concepts related to #categorytheory.

https://abuseofnotation.github.io/category-theory-illustrated/

#sets, #categories, #monoids, #orders, #logic, #functors

Credits: @abuseofnotation

20 years ago I was at a CS conference in Cambridge UK and asked a grad student in CS theory there to explain #monads to me. "Are they related to #monoids? " I asked. The response was incomprehension because monads were studied, but monoids were not even mentioned.