Run it at https://xin-xin.me/code/factor/
This simple Javascript app factors all numbers <= 9007199254740991.
With multiple numbers, it will find the greatest common divisor of the numbers.
$ git clone https://github.com/xinxinw1/factor.git
Then, open index.html in a browser.
Alternatively, click index.html in Github, right-click "Raw", click "Save Link As...", and then open the file.
This program is dedicated to the public domain using the Creative Commons CC0. See LICENSE.txt for details.