AlmostVPN is an SSH tunnel manager with a twist. It is packaged as a Preference Panel, so you do not have to use yet another application to configure your tunnels. Instead, it uses creative network configuration techniques to provide almost VPN-like access to remote services, so you can keep using real IP addresses and port numbers while accessing service on the other side of your tunnels. It provides a simple way to mount remote volumes, use remote printers and faxes, access iTunes, iPhoto, and almost any other Bonjour-based application, transfer and execute files, and more.
Alt+Connect manages dialup connections, allowing a group of networked machines to share a single Internet connection through their server. Custom client software lets users to start or stop their internet connection, and the server (connectd) ensures that the connection remains up only while someone's using it. Features include support for multiple ISPs and links (modems or ISDN channels), connection control lists, ability to record the time a user spends online and charge him for it, and the ability to enable and disable IP forwarding as a machine starts or stops using the Internet.
chownat allows two peers behind two separate NATs and firewalls to establish a direct connection with each other. No port forwarding, DMZ, third party, proxy, spoofing, elevated user privileges, or DNS tricks are required. More importantly, it opens up a tunnel between the two machines so one peer can access a service, such as SSH or a Web server, on the other machine which is also behind a NAT.
If you ever noticed how your SSH/gaming sessions become sluggish when you start downloading something, or how your downloads slow down when you start uploading, and your broadband link is managed by a Linux router/gateway, then you could benefit from using CTShaper. CTShaper reduces link latency by reducing queueing on your side and on your ISP's side. Additionally, it sets up four traffic queues with different priorities and (configurable) flow rates.
DAXFi is a Python script that helps configure several different kinds of firewalls in a consistent way. It can run as daemon to adapt its behavior to external conditions; rules can be described with XML files, XML strings, or generated directly by the code; the program can be configured and extended with a sort of plug-ins written in Python. It comes with a Python package, useful to build other applications aimed to manipulate different firewalls in a uniform way (some example programs are included).
DummyIdentd Server Daemon is a Perl program that accepts identd requests (port 113), and responds with a valid response, but giving out no useful information. It is written in Perl, and is suitable for running on company gateways/firewalls to enable your users to access services such as IRC, which require identd.
etherdam is an IPTables firewall configuration engine. It implements a primitive (and hopefully simple) scripting language as an alternative to the direct use of iptables. It comes with full documentation plus a heavily-commented example config file. The config file should work for many scenarios with minimal adjustment.