GNS3 (Graphical Network Simulator-3) is a network software emulator that allows users to simulate complex networks. It is widely used by network professionals and students to design, configure, and troubleshoot network topologies without the need for physical hardware. GNS3 supports various network devices, including routers, switches, and firewalls, enabling users to create realistic network environments. The platform is compatible with multiple operating systems and integrates with real devices, making it a versatile tool for learning and testing. Users can also connect GNS3 to VirtualBox or VMware to enhance their simulations, providing a comprehensive learning experience in networking concepts.