The windows version is an add on called a "power toy" from Microsoft.
They are all here:
Windows Power Toys
Here is the direct link to the Image resizer:
ReSizer
And some helpful instructions here:
Photos
One of the disadvantages of the free one is your choices to resize are only "small, medium, and large". You have to play with them based on the size of your file to start with, and the file size you want to end up with.
Not as feature rich as the other programs that Ed has suggested.
Enjoy,
Fritz.