PS-MRTG
MRTG-style bandwidth monitor for Windows, one PowerShell script
...Counters are read through Get-NetAdapterStatistics, usually without admin rights, so it runs on locked-down and offline machines as well as ordinary ones. It works with ConstrainedLanguage, Windows PowerShell 5.1 and PowerShell 7+, and adds a CSV export and a configurable alarm threshold.
Free and open source, MIT licensed. Code on GitHub, also on the PowerShell Gallery.