This was a challenging one for me, since I usually use lots of color. I went with an "*" as the shape and played with transparency, size, and movement.
Made an explorer for "elementary cellular automata"!
By moving the mouse, you can change the Wolfram code (which defines, in bits, a table for how to compute a pixel from the previous line).
This also was the first time I've tried the #fennel language – a Lisp that compiles to Lua! #tic80 has several of these niche little languages built-in! <3