The software is said to be compatible with Snow Leopard 10.6 or greater which means that you should download the Mac version from the official website to proceed to its installation. Unfortunately, that's the only version available for download. If you need help with it, I recommend downloading the manual as well.
However, if the software refuses to install and run on El Capitan, then forward this bug to the developers, and they should take care of it if the software is still in development.
Official website: http://www.openeye.net/products/software/remote
Contact US: http://www.openeye.net/contact-us