Each simulator sits inside the lesson that teaches its topic, so the explanation is right above it. They are simplified educational models of documented FortiOS 7.6 and FortiManager 7.6 behaviour, not emulators: they show the order of decisions and the result, and name the command that shows the same thing on a real device. Nothing moves until you click.
- Packet flow explorer in Understanding FortiGate firewall packet flow
Follow one packet through ingress, session lookup, destination NAT, routing, policy, inspection, source NAT and egress, for new sessions, replies, a VIP, a deny, an RPF drop and offload. - Policy matching simulator in How firewall policies work
Test connections against a policy table and watch FortiOS check each policy top-down, criterion by criterion, until the first match or the implicit deny. - NAT simulator in Source NAT and IP pools
See addresses and ports change in both directions for interface SNAT, IP pools, virtual IPs, port forwarding and central NAT. - IPsec tunnel simulator in IPsec VPN concepts
Step through IKEv2 negotiation and ESP data between two FortiGates, then break it: proposal or key mismatch, selectors, blocked ports, NAT, missing route or policy. - HA failover simulator in High availability (FGCP)
Set priorities and override, then fail links and units in an FGCP cluster and see which FortiGate becomes primary, and why, and what happens to sessions. - FortiManager install workflow in The Fortinet product family and the Security Fabric
Register a FortiGate, change a policy package, preview and install it, and see what happens when someone changes the FortiGate locally.
To try the same things on real software, use a FortiGate VM in a lab. The lessons' practical exercises say what to configure and which output to compare.