Most 3rd party Kontakt sample file downloads are usually encoded as a rar file.
What is your favorite software to decode these files?
Free or low cost preferred. 
Windows 10.

uh, WinRAR.
 
download the 30 day full trial and when the trial is up you can still use it free to unrar files.
 
official website with download is:
http://www.rarlab.com/
 
 

I use 7zip, not because it's anything special but I've used it for years without issues.

MachineClaw
uh, WinRAR.
 
download the 30 day full trial and when the trial is up you can still use it free to unrar files.
 
official website with download is:
http://www.rarlab.com/
 
 

+1
Been using it for about 5-7 years now....free version.

bitflipper
I use 7zip, not because it's anything special but I've used it for years without issues.

Same here, been using and recommending it for years as well.  Plus (as the name implies) it extracts zip files too.
 
So, it handles rar and zip files (and other compression formats) with ease -- and it's free. 
 
Don't know why you'd need to go with anything else.

Thank you, everyone. Solved.
7-zip is my choice.
It is free, non-commercial, and has a nice browser/GUI for ease of use.
 
Be aware that windows 10 put up the red warning box saying something like this:
"This type of software is not normally installed, would you like to install anyways?"
 
I clicked "yes", installed, then ran a virus check and all is good.
 
 

+1 winrar
I've used it for years.