3blue1brown, or 3b1b for short, is primarily a YouTube channel about discovery and creativity in math. On this site, you can find written versions of many of these lessons, often with more interactive elements sprinkled in.

In terms of implementation, though, it is far from simple. Lambda calculus has variables, which introduce huge complexity into the interpreter: especially if you want to do any kind of formal reasoning about programs, this complexity is a problem. We might want to reach for something even lower-level than lambda calculus: this is where combinator calculi come in.

Category Theory Illustrated is a primer in category theory and other mathematical theories that is made to be really accessible to people with no prior exposure to the subject, without being dumbed down, by utilizing visual explanations.