BWM-NG - Network Bandwidth & Disk I/O Monitoring
Bandwidth Monitor NG (bwm-ng) is a simple small console based live Network and Disk I/O Bandwidth monitor for Linux, Unix, BSD,Solaris, Mac OSx, Windows based platforms.
There is no fancy GUI or interfaces simple console utility which installs and runs flawlessly showing live stats of your Network or Disk I/O stats.
Disk I/O support is only added in the latest stable version bwm-ng 0.6 and Disk I/O is not supported on Windows Platforms yet.
Nagios Checker - Nagios Alarms on your Firefox Status bar
Just came across this great Firefox Browser addon, Nagios Checker 0.11 for Nagios Network Monitoring system alerts. This is a great simple addon that shows any alarms on your nagios monitoring system simply on the browser status bar providing the need not to logon to Nagios web interface. The extension loads up in the status bar and alarms you of any network events. What I liked in the extension is that it is absolutely non-intrusive. Sits on the bottom right corner of the browser status bar and highlights any alarm. When you move your mouse over it, it displays the alarm in detail.

