Tree Calculus is a minimal, Turing-complete, reflective, and modular calculus discovered by Barry Jay. It has one operator that computes whenever it is acting on three values, and its values are natural binary trees. The calculus has practical consequences such as trivial and safe interpreters on any platform, and it is a good fit for cross-platform configuration generation. Tree Calculus also allows for the representation of recursive functions as normal forms using fixpoint constructions.