Join calculus is described here as defining a set of chemical equations that can all take place anytime within a soup of molecules. This is used in JoCaml to organize concurrent logic and distributed logic, as an alternative to the actor model in Erlang.
Fwiw, a more formal overview of join-calculus aimed at programming language researchers (rather than intended as an introduction to programming in JoCaml) is in this 2002 paper (pdf). As the linked tutorial notes, the paper doesn’t use the “chemical” metaphor and uses more classic process-calculus terminology instead.
A quick skim shows some similarities to FRP or Data-Flow Model. Those have mature implementations already. Ill read this later, though.