Ledcontrol is a program that shows information on the normally-unused LEDs on your keyboard. You can configure it to show virtually any TRUE/FALSE condition or arbitrary value accessible. Features include blinking LEDs, priority levels, user-made animations, a GTK+ interface, etc. Ledcontrol works both in X and on a text console.
Angst is an active sniffer, based on libpcap and libnet. It dumps into a file the payload of all the TCP packets received on the specified ports. It implements two methods for active sniffing. Angst is able to monitor ARP requests, and after enabling IP forwarding on the local host, it sends ARP replies mapping all IPs to the local MAC address. Also, it can flood the local network with random MAC addresses (like macof), causing switches to send packets to all ports.
Rain's PPP scripts simplify the use and setup of pppd. Features include connection time logging, a ppp-off that works right with more than one pppd running, dial-on-demand support for pppd 2.3.x., and more. Another interesting feature is that the scripts keep track of your connect speed and time, and included is an mirc script to show connection status from a remote machine, as well as a shell script that works for *IX boxes.
TUN provides packet reception and transmission for user space programs. It can be viewed as a simple Point-to-Point or Ethernet device, which instead of receiving packets from a physical medium, receives them from a user space program and instead of sending packets via physical media writes them to the user space program.