An advanced network simulator to design and configure virtual networks
Build, Design and Test your network in a risk-free virtual environment and access the largest networking community to help. Whether you are studying for your first networking exam or building out a state-wide telecommunications network, GNS3 offers an easy way to design and build networks of any size without the need for hardware.
rsim is a simple discrete-event communications network simulator initially developed to test routing protocols for undersea acoustic modem networks. If done well then rsim will eventually be a good replacement for "ns2".