tcptrack is a sniffer which displays information about TCP connections it sees on a network interface. It passively watches for connections on the network interface, keeps track of their state and displays a list of connections in a manner similar to the unix 'top' command. It displays source and destination addresses and ports, connection state, idle time, and bandwidth usage.

Wietse Venema's network logger, also known as TCPD or LOG_TCP.

Hardware Locality (hwloc) provides a portable abstraction (across OS, versions, architectures, ...) of the hierarchical topology of modern architectures. It primarily aims at helping high-performance computing applications with gathering information about the hardware so as to exploit it accordingly and efficiently.

Munin is a highly flexible and powerful solution used to create graphs of virtually everything imaginable throughout your network, while still maintaining a rattling ease of installation and configuration.