I love L-Systems. I somehow obtained a couple of VHS tapes in the 90s when I was a kid of early computer graphics, and was really taken by the generative artists — like Karl Sims. This was also the heyday of big bookstores like Borders, and I’d spend hours in the “Computers” aisle, where I found “Advanced Animation and Rendering”, which covered L-Systems.
These are fun things to code because they can surprise you. Even when you understand the rules, it can be delightful to see what grows.
Someone coded procedural swimming with simulated tentacles. The post itself is a video and then they tell a little bit about it in the comments section also.
I used to frequent a website with nearly a hundred experiments like this, almost all interactive and very beautiful. They were all created with Flash/ActionScript. There were lots of tree visualizations, fluid simulations, and one specific demo with randomized bugs that walked around using inverse kinematics. I've since lost the link, does anyone remember what I'm talking about, maybe could provide a link?
These are fun things to code because they can surprise you. Even when you understand the rules, it can be delightful to see what grows.