Nano VNA saver (good source) -
https://github.com/NanoVNA-Saver/nanovna-saver/releases/

TESTED SO FAR ON -

Linux Mint 18.3 - Doesn't work on my system at all.
Linux Mint 19.3 - OK
Linux Mint 20.0 - Not tested yet.

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NOTE - On Linux please ensure that you have set yourself up to be able to use your own comports.
You need to add yourself to the dialout group.
In terminal the command is "sudo usermod -aG dialout username" and then REBOOT !!
Down the bottom left hand side of the program press the connect to device button.
The software for some reason usually exits (don't ask why).
This is a good sign, because when you restart the software and attempt to connect it all works ok.
Strange but true.