This work describes the development of an optimizing tool as help for the basic engineering of Organic Rankine and Steam Rankine cycles. Steam Rankine Cycles, or in this work called SRC's, are well proved for high temperature flue gas. Here the work gives a tool to calculate the basic variables for the design of such a facility. The so called ORC cycles are able to produce energy from low grade heat and can be a step forward in today's economic and environmental issues. For the ORC processes the improvement in technology leads to the possibility of using this cycle in the supercritical area. A possible lower entropy destruction results in higher power output as well as a higher thermal efficiency what is shown in the simulations at the end of this work. The tool is build up on an Open Source Programming language called PYTHON and gives choices between sub-, supercritical Organic Rankine, single pressure and double pressure Steam Rankine cycles. The various outputs, calculated from a given heat source data, can be used for further works in cost calculation or design of heat exchangers what is not part of this essay. This work also describes the usage of the optimising tool and errors that can occur.