This is Mac specific, but I recently found Rubbernet. Its a really great app that allows you to see the per application network usage of your Mac plus it supports Remote Monitoring. You can install a Rubbernet plugin any Mac that you have administrative access and then monitor the per application bandwidth utilization of all the Macintosh on your network from your own computer.
It does cost money (30 Euros on their website but for some reason its $19.99 on the Mac App Store but they have a fully functional Free Trial on their website. I haven't bought the app yet, so I can not confirm that you can buy one license for the app and then install the plugin on any number of Macs for now additional charge. But that seems to be the situation.
The Developers are the same folks who do the Linkinus IRC Client.
Another option that is not quite as good as it does not have any kind of remote monitoring mechnaism and didn't seem to do as good a job is OS Track. Its also available on the Mac App Store for free.