trafcnt is an IP accounting scripts for a small LAN. It parses logs created by IPFM or any simillar source and calculates usage costs. It is possible to describe different schemes of operation for different users or groups. OpenBSD's pfctl is used for FW\NAT control, but trafcnt could be easily adapted to use almost anything. It produces clf- style logs.
Trafmetux is a network traffic meter for Linux. It tells you how much IP traffic has been seen by the Linux kernel module during the last few minutes, hours, days, weeks, and months. It's very useful when you have a limited Internet connection with quotas. For instance, many mobile broadband ISP provide only 3GB/month. In that case, you need to know how many megabytes you already used.
Treeps is program for Unix/Linux that is designed to make monitoring and interacting with the running programs on your system easy and intuitive. A "real time" tree view shows the relationships between the processes and is color-coded to provide easy interpretation of various values. The process tree displays any combination of users/groups and can be used to drill down into process details and then extract key fields for continuous monitoring. A number of actions can be performed on processes, such as signal, renice, trace, view man page, etc.