Create a wifi hotspot
Provide Wifi access from wired ethernet (Access Point)
iptables-restore < iptables.ipv4.nat.eth0
Provide wired ethernet access from wifi (gaming adaptor)
iptables-restore < iptables.ipv4.nat.to-eth0
Give Wifi access from another Wifi AP (e.g. BTWiFi-with-FON)
iptables-restore < iptables.ipv4.nat.wlan1
Ready made SD .img at https://sourceforge.net/projects/pi-ap/