We have a free version of ZBrush called ZBrushCoreMini!
This Maxon page has detailed information about ZBrushCoreMini here as well as download instructions!
After you have registered, you will then need to download the installer from the Downloads page at My.Maxon.net. ZBrushCoreMini does not install using the Maxon App.
If you have any further questions about ZBrushCoreMini after reviewing the above page, please feel free to contact Maxon Support via a support ticket and we can assist you further.