From Paessler development team:
Today we have released version 6.0.6 of PRTG Traffic Grapher. This version mainly adds the new feature of aggregate graphing (see this blog entry for details), some performance improvements for large installations as well as a number of bugfixes and smaller changes (see PRTG's history page for details).
The latest version can be downloaded from the PRTG download page.
PRTG Traffic Grapher is an easy to use Windows software for monitoring and classifying bandwidth usage. It provides system administrators with live readings and long-term usage trends for their network devices. The most common usage is bandwidth management, but you can also monitor many other aspects of your network like memory and CPU utilizations.