Systems which allow interacting particles with string representations, that interact. Distributed or agent-based models for stringology. This might remind us of evolution, or chemistry, or computational learning agents or whatever. Is there a name for this family of systems?
These are popular as models for… Understanding what kind of computing nature might be doing? Or as a source of biomimetic algorithms. Other? Perhaps one-day making ubiquitous natural computing possible?
P-systems and membrane computing
Probabilistic, Turing-complete artificial chemistry. Well-documented elsewhere.
the Broadcast language
John Holland's candidate generic Genetic Algorithm system which is supposed to be Turing complete, if not quite as elegant as it wants to be.