What's your side hustle?

I'm curious to hear about the side hustles that I hear so much about. I see a lot of comments about people making income outside of their 9-to-5. I've considered it many times, monetising some of my hobbies so I'd love to hear more. Are these hustles related to your main job role or completely different? Do they take up a lot of your spare time? How did you make it successful?