I hop use the CDROM-distrubution Knoppix to do what as a Cisco router do with a little bit configuration, better have a graphic software setup enviroment.

1.Support mutilple NICs--more than two;
2.There are some access polices can apply inbound or outbound or both side of the NICs in the network layer of the OSI model;
3.Support the different subnet can shared the internet connection as a NAT does;
4.Support the different local subnet can communication with each other--can route the packet from the different subnet.