Then you better take a look at this:https://github.com/influxdata/telegraf
It collects and generates metrics. In and of itself it doesn't do that much, but you can add already available plugins to collect the metric you need, or write your own.
Having seen reports you can generate with it, it is very interesting. Not sure it does tray notification though.
Then there is also the built-into Windows itself Resource Monitor. You can select the resource you wish to monitor, and there is a tray notifier.
DiskMon from SysInternals might prove useful too. Just as Process Monitor, also from SysInternals. This tool shows you resource usage of processes (duh), including CPU, RAM, disk I/O, network I/O, handles etc. Process Monitor can activate a tray notifier as well
All of the tools mentioned here are freeware.