On Windows: Sysinternals Process Explorer, already mentioned Glasswire and NetBalancer and a bunch of other apps, almost all which aren't very good at all. But Glasswire is very nice.
Also from Windows 8 and up the built in task manager has per process network usage along with disk usage. Makes it real easy to find bottlenecks or resource hogs.
Does this require Administrator rights to see this granularity? In my office as a non-admin user, we have noticed that Task Manager seems really crippled.
You won't see other users processes, at least on my box however the detail is there for yours. Probably possible for it to be crippled by group policy.
In previous versions of Windows, the task manager menus could be toggled by double clicking an empty area in the window. You should also be able to select additional columns to display in the options. Note: I haven't used the win8 taskmgr.