Plotting functions (usual and parametric) with more possibilities. Differentiation of any order (with simplification). Construction of tangents to the graph. The simple and clear interface with the detailed documentation and examples of work. The program is designed both for inexperienced and the professional user as in it are combined the intuitive interface and professional functions. FlatGraph allows: - To enter one or several functional expressions of any complexity for display and (or) their differentiation; - To carry out symbolical differentiation for the specified order of a derivative, and also to carry out simplification of the received derivative; - To investigate \"alive\" changing of various parameters of functions with simultaneous display of new graphs that allows to define influence of parameters of functions on their form; - To use automatic or manual scaling schedules of functions for linear scales; - To display parametric functions, for example, ellisoid, cardioid, Bernoulli lemniscate and other similar graphs (where abscissa and ordinate depend on one parameter \'t\'); - To solve the equations, system of the equations and inequalities by graphic way; - To define and display a tangent to the graph of function in a point x0 (it is set by the user). FlatGraph has the simple and clear interface, detailed user guide and examples of work.