ipt-netflow is high performance NetFlow exporting module for Linux kernel (up to 3.x). It is designed for Linux router with heavy network load. This is netfilter/iptables module adding support for NETFLOW target. It is designed to work without conntrack. It supports NetFlow protocols versions 5, 9, and IPFIX. It has accounting for IPv4, IPv6 traffic, and (NEL) NAT translation events.
linux_ics is designed to make the process of sharing an Internet connection from a Linux computer easier for the average user. It handles configuring the interfaces, setting up NAT, and optionally running a DHCP server. In addition to Ethernet, linux_ics can also share an Internet connection over a WiFi interface in either ad-hoc or master mode.
otonat is a 1:1 NAT implementation for FreeBSD. Unlike other solutions that keep state for individual user connections even for 1:1 NAT, otonat is completely stateless as far as user connections are concerned. This allows it to scale much better and provide protection against misbehaving clients that may consume a lot of server memory by opening too many connections.