The Living Thing / Notebooks :

String dynamics

A marshaling point for several loosely connected models in discrete mathematics, based on free monoids.

Symbol processing systems, automata, symbolic dynamics for dynamical systems, strings of DNA. Languages. Finite state Markov machines. Syntactic machines. Systems of strings of symbols. Artificial chemistry.

The Turing machine and λ-calculus are classic examples, but there are many ways of operating on strings of symbols.

For some useful metrics on strings, see spaces of strings.