Can I download OptimizePress to more than one computer?

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.