Network Simulator is a free software that can be used for making Network Topologies and educational proposes. Software designed and Programmed by Hesam Haddad.
Network Simulator Properties
Network Simulator is built in C#.Net environment, and published in .Net Framework 3.5 and .Net Framework 4. Due you have .Net Framework 3.5 in windows 7 and .Net Framework 4 in windows 8 by default there should be no worries about incompatibility with your system.
Network Simulator feature