I certainly can believe that you would might be missing software that exists on one OS and not another (I know I'm often shocked what (to me) critical software either doesn't exist and or doesn't work well on Windows), but I'm surprised that it's system monitoring software in particular, given the existence of psutil (which is indeed crossplatform) and other such tools on Linux and the propensity of Linux users to want to know stats about their systems.
I mean psutil itself is likely less end-user-focussed than what you want, but I would have expected someone to have used psutil or something like it to build a user-facing tool monitoring tool that covers the full range of things one might wanted to be monitored. For instance, is CPU-X missing functionality you're looking for?