Need Network Monitor Recommendation

Specifically I am looking for a software only solution, that will tell me which devices are using bandwidth on the home network and how much of the bandwidth per device. Something simple to use, I'm pretty tech savvy, but this is really just going to be for rooting out existing problems.

This is a relatively new problem, but we have a lot of devices and I am trying to determine if this is the result of bandwidth reservations being made by the router for all of these devices, or if it is specific behavior by a certain device, or if it is user created i.e. downloading/uploading/streaming etc.