Rhyscitlema Calculator is an application to evaluate expressions expressed in the Rhyscitlema Function Expression Text (RFET) language. RFET enables the representation of mathematical expressions in plain text in simple and effective ways. Instead of only thinking of a single-value, vector or matrix, the fully general value-structure is used: an example is (1,(2,3,4),5). RFET enables evaluating simple expressions such as 1+1, to evaluating advanced expressions such as 2*f(3); f(x)=4x, to evaluating highly complex expressions in an Object-Oriented Programming model (using inheritance and encapsulation). This software is at the core of the Graph Plotter 3D software.