GNS3 is a free application released under the GPLv3 license on Windows from network auditing software.
Security: Secure your networks with firewalls and other security devices.Scripting: Automate network operations with Python and other scripting languages.Routers: Support for a wide range of Cisco routers.Protocols: Use a range of network protocols in your simulations.Networking: Design and simulate complex network topologies.Images: Use Cisco IOS or other images to build networks.Export: Export your simulations to other cloud and virtualization platforms.Collaboration: Share designs and simulations with anyone in real-time.Cloud: Integrate cloud services into your virtual networks.GNS3 does not do that and you can run hundreds of devices in a GNS3 topology (assuming you have the hardware to do it). Other solutions like Cisco VIRL limit the number of devices in a topology to 20 Cisco devices (depends on license). You are only limited by the hardware resources you have available. GNS3 does not limit the number of devices you can run in a topology. It uses Dynamips emulation software to simulate Cisco IOS. GNS3 is a network software emulator that allows the combination of virtual and real devices, used to simulate complex networks its name is comes from Graphical Network Simulator. Network topology simulation software designed for professionals