SmokePing keeps track of your network latency:
* Best of breed latency visualisation.
* Interactive Graph Explorer.
* Wide range of latency measurment plugins.
* Master/Slave System for distributed measurement.
* Highly configurable alerting system.
* Live Latency Charts with the most 'interesting' graphs.
* Free and OpenSource Software written in Perl written by Tobi Oetiker, the creator of MRTG and RRDtool