The design of network protocols is greatly accelerated by the use of simulators particularly when studying a protocol?s behavior in a large internetwork topology. However the accuracy of the simulation results are heavily affected by the input network topology. As taking a real map as an input is not always feasible, artificially created topologies are often used. There exist many network topology generators available but recent discoveries on the Internet topology have made most of them obsolete when it comes to model a typical part of the Internet. This paper presents a free open source software designed for network topology analysis and modeling called network manipulator (nem). It is capable of creating realistic Internet - like topologies and it can check proof them on the fly by a thorough topology analysis. The paper especially focuses on the architecture and the capabilities of the software.