GNS3 - GNS3 is a graphical network simulator that allows simulation of complex networks.
OpenDaylight - OpenDaylight is an open platform for network programmability to enable SDN and create a solid...
ns-3 - a discrete-event network simulator for internet systems
Ubiquiti UniFi - UniFi is the SDN platform for Ubiquitis UniFi series
NetSim - NetSim software was created to simulate various Cisco systems. Cisco software is known around the world as being one of the best network, routing and switch systems for businesses and private use. Read more about NetSim.
Beehive SDN Controller - A distributed SDN controller with OpenFlow support