Many routing protocols have been developed to improve the lifetime, bandwidth reusability and scalability of the Wireless Sensor Networks (WSNs). The operation of routing protocols is difficult to understand and some problems may occur while developing these protocols. Simulation is a relatively fast way of estimating these protocols and understating what is happening in the network. Thus, this paper presents an open source Graphical-based educational simulation tool called Gbest-WSN for simulating routing protocols of the static and mobile, homogeneous and heterogeneous WSNs. Gbest-WSN tool has a user-friendly interface that helps the user to select the routing protocol and define the network configuration. It is provided with four routing protocols; namely LEACH, LEACH-Mobile, immune algorithm-based and genetic algorithm-based routing protocols. Also, it allows the user to update the existing routing protocols and add a new routing protocol. Gbest-WSN is provided with radio, coverage and mobility models for modeling the hardware of the sensor node. It shows a detailed 2D and 3D graphical perception for what is happing during the routing process. Also, it has the ability to compare the simulation results of different simulation methods or different network configurations. In addition, it allows the user to save and load simulation scenarios and also exports the graphical results on PDF files and the statistical results on excel or mat files. Moreover, Gbest-WSN is provided with html help documents to help the user how to use it. The illustrative simulation examples clarified that the Gbest-WSN is a helpful tool for the students, teachers and researchers who work in the field of WSNs.