Thanks for your response, and the links.
I have two widgets folders on my MacBookPro (OS10.6.8), one is HD/Library/Widgets, and the other is User/Library/Widgets. All of the widgets I have are in either of these two folders except one.
The missing widget is still active and useful in dashboard. When I launch dashboard it is there and I can use it. So I want to install it on my new MacBook (OS Sierra), but I can't find it to download from the internet, and I can't find it on my old computer to transfer it over.
Part of the reason I can't find it is because I don't remember what it is called. It doesn't display its name in dashboard, and it is obviously none of the ones listed in my widgets folders.
It's a widget that scans local wifi networks and tells me the name, strength and channels they are on. From memory it is called something like "wifi tracker"... and I got if from the Apple widgets site a couple of years ago.
I know Sierra may offer this kind of function, but I want it as a widget.