https://p5js.org/examples/
The Spirograph example on p5.js was one of the most particularly interesting to me because of its inherent complexity. The interlocking circles (sines), produce an interesting time system in my head, that reminds me of how our time definition works accordingly to the solar system, in that each large circle cycle could equal a year, each medium could be a day, and so on and so forth. Additionally, I found it even more mesmerizing when the underlying geometry was hidden, and instead, only the tracing remained.
One library that I found particularly interesting (as with what seems like the rest of the world is interested in now too, it seems) is the ml5.js library, or, the machine learning library. Not only was this one of the better documented and more user-friendly crafted library sites to view, it was interesting enough that it was marketed as "Friendly Machine Learning for the Web" -- and as a "neighborly approach to creating and exploring artificial intelligence in the browser", which made it not only extremely friendly, but made it feel as though machine learning would be the new ubiquitous thing.
https://glitch.com/~friendly-
"Friendly Words" is an interesting Block on Glitch -- it randomly generates a list of "word pairs" (which I feel are common for p5js web files), predicates, objects, team synonyms, team pairs, collection synonyms, and collection pairs. I thought this would be particularly helpful when generating random auto file names that have a bit of character for programs such as p5js and glitch, and/or random anonymous user names when entering as a guest into communal platforms (such as Google Docs).