Ready to use OpenWRT NAT router appliance for ©VMWare ©ESXi.
You only have to uncompress and register it to your ©ESXi server to be able to use it as a fencing device between your LAN network and some NATed network inside your ©ESXi host.
It can also be easily configured to serve as a firewall in a dedicated ©ESXi host.
You can follow the setup guide at https://33hops.com/vmware-esxi-nat-with-custom-firewall.html
The appliance comes in a very small package (less than 5 MB), still...