OptimizePress is a WordPress based application (comes in Theme and Plugin formats) – so you install and run it on your own server/hosting – not on your local computer.
You can of course download it to any computers you have ready to upload to your websites – but you need to be aware that it doesn’t actually run on your computer it runs on your hosting/Wordpress site as it requires WordPress to run.
You can find more information about OptimizePress and how it works by watching the OptimizePress introduction video in the members area.