ntop version 2 is a tool to sniff traffic on the network and display
statistics about it. It has a built-in web server for displaying the
results of the data it collects, and it can also generate data in
various formats (such as NetFlow) to be passed on to other systems.

Note that version 2 of ntop is significantly different from version 1.
It is much larger and has many more features. If you're looking for a
more light-weight tool, you may find that version 1 (the "ntop" package)
suits you better.