WOW!!!!!!! I just unzipped over a thousand files in about a half hour.
The name of the freeware is Unzip ThemAll.
I had heard of it, but had not tried it. I tested and tested, and so far - works great for me.
One tip - put zip and rar files in separate folders. When you are unzipping a batch of zip files (for example), if there are rar files in the folder, the job stops with an error code message (when it comes up to an rar file) and you have to click ok to continue. When I moved the rar files to another folder, things sailed through. And then when I did my rar files in separate folders, it breezed through them too.
What I did tonight, would have taken me WEEKS or MONTHS to go through.