libnetfilter_cttimeout is an interface to Netfilter Connection Tracking timeouts. It provides a userspace library which provides a programming interface to the fine-grained connection tracking timeout infrastructure. With this library, you can create, update, and delete timeout policies which can be attached to traffic flows.
OpenFWTK is an application proxy toolkit which inherits the ideology of TIS fwtk and maintains API backwards compatibility. The design goal is to make it simple yet powerful; no performance hacks are allowed in the code and library dependencies are reduced to a minimum. It is a true application layer filter. It features unified pluggable content inspection for the most frequently used protocols, NAC (Network Admission Control), and the ability to define fine-grained Internet access policy based on browser identification.
The MiniUPnP project is a library and a daemon. The library is aimed to enable applications to use the capabilities of a UPnP Internet Gateway Device present on the network to forward ports. The daemon adds the UPnP Internet Gateway Device functionality to a NAT gateway running OpenBSD/NetBSD/FreeBSD/Solaris with PF/IPF or Linux 2.4.x/2.6.x with netfilter. One of its most interesting features is to enforce some permissions to allow or deny redirections, bringing some security to UPnP. Newer versions also support the NAT-PMP protocol from Apple.
Trustix™ Enterprise Firewall is a WYSIWYG firewall for iptables. It provides drag and drop security policy deployment and allows you to visualise DMZs, integrate branch offices with 3DES encrypted VPN tunnels, accelerate Internet access times with proxy caching server, and authenticate remote workers with PKI X.509 certificates. The unique GUI also allows you to manage traffic for all your zones (up to 24) as well as port forwarding and network address translation (NAT).