A new and simple network simulator Nessi is described in this paper. While other simulators focus on minimizing the simulation time, Nessi tries to minimize the development time and the difficulties to implement a new simulation model. As such, it is mainly oriented toward educational use, where it enables students to implement or modify simulation models of protocols with minimal overhead. A second application of Nessi is for verification and performance evaluation of new protocols, where it allows the developer to easily explore different options. Nessi comes with an easy to use graphical interface that allows the user to interactively monitor the behavior of a simulation, to modify simulation parameters and to plot results.