This paper introduces PeMSyn, a free tool intended to aid the design and simulation processes of permanent magnet synchronous machines. Using PeM-Syn, one can effortlessly design a permanent magnet synchronous machine, design its winding distribution and assess the machine performance. The machine performance is evaluated by means of FEA since PeMSyn provides an interaction between Matlab and FEMM. Thus, several machine parameters can be obtained. Another interesting characteristic of PeMSyn is its modularity, which means that each functionality can be run independently and new functionalities and machine topologies can be added either by the user or by means of a new PeMSyn update. Aiming to be simple and user-friendly, PeMSyn was coded in Matlab language in form of a graphical user interface (GUI). Moreover, users can easily translate all labels and variable names to their mother language using a language description file already available in English and Portuguese. The modules, the machine design process, the equations involved and an application are shown in this paper. In order to present guidelines on how to use PeMSyn, an example of machine design is proposed and its performance is assessed.