Looking through the p5js reference, the functions about drawing shapes caught my eye because I haven't made my own polygons before, I've always just used quad or ellipse or whatever. So the beginShape(), vertex(), and endShape() functions are something I'll definitely plan to use more. I also looked at beginContour(), which is used for negative spaces within the shape you're drawing, which would've been nice to know about when I spent some time in my clock project trying to draw a ring. Here's the beginContour() reference.

Out of all the p5js libraries, I was most interested in p5bots, which allows you to incorporate input from microcontrollers like Arduinos into your sketch. I've never used Arduino before, but I'm interested in trying, and once I learn more about it, it'll be cool to be able to use it with p5js.

This online socketio chatroom is really cool, and chatrooms have a lot of potential. I was reading an article about someone who found an API for Tinder and would catfish guys then have them actually be messaging with each other instead of the girl. Here's the article I read. Manipulating people's chats could be very powerful if done carefully.