The add-on is freely available on other platforms. The $1 price tag for Blender Market gives you access to their download manager, and a percentage of that will go towards the Blender development fund.
To get the add-on for free, check the description of the introductory video.
Occasionally, some people have issues with add-ons not appearing in their user preferences after installation. This can happen for any number of reasons. The first things to check are:
- Are you using the correct version of Blender? (2.8)
- Do you have the latest version of Python installed on your computer?
- Have you tried a manual installation of files by moving the BY-GEN folder into the addons folder within Blender's local application data.
For more assistance with installing add-ons, please visit this page.