Nmap - Nmap Free Security Scanner, Port Scanner, & Network Exploration Tool. Download open source software for Linux, Windows, UNIX, FreeBSD, etc.
iftop - iftop does for network usage what top(1) does for CPU usage.
SolarWinds Network Configuration Manager - SolarWinds is a leading provider of powerful and affordable IT infrastructure management software. Make IT look easy.
vnStat - vnStat is a console-based network traffic monitor for Linux and BSD that keeps a log of network...
Cisco Network Assistant - Cisco Network Assistant simplifies wired and wireless network management, and provides critical product information using Cisco Active Advisor.
darkstat - darkstat is a packet sniffer which runs as a background process, captures network traffic...