RapidExpCart is a shopping cart system composed of two programs that consist of a WordPress plugin and a main program. So, you should download the main proguram from rapidexp.com besides this plugin.
The main proguram needs the following system requirements.
- php5 + mysqli (module mode is recommended)
- MySql5 (InnoDB is recommended)
- mod_write
And then, … it is only Japanese at present 🙁