Hi Zero,
I'd like to find one too !
This video explains already a lot (just skip the details for implementation in Processing) :
https://www.youtube.com/watch?v=f6ra024-ASYAlso :
https://en.wikipedia.org/wiki/L-systemAnd you can google this "PDF: The Algorithmic Beauty of Plants" and get the book by Aristid L* himself.
BASICS :Axiom : F (axiom means iteration #0, here F is a straight horizontal line to begin with)
Rule : F=F+F--F+F (replacement)
Angle : 60°
That means that at iteration #1, you replace initial F by four F segments, with + being a rotation by +60°, - by -60°.
And so on. That gives :

--
Now if you replace the axiom above by this one (keeping the same rule and angle) :
Axiom : +F--F--F (i.e. iteration #0 is a triangle)
...after some iterations you will get a nice snowflake :


You can practice on-line here:
http://www.kevs3d.co.uk/dev/lsystems/