This is an osCommerce 2.4 Related Products App on which you can base your own App
It is based on the osCommerce documentation here https://library.oscommerce.com/Online&en&oscom_2_4&developers&apps and the tutorial I wrote at http://forums.oscommerce.com/topic/410863-how-to-make-a-24-app/. Make sure you refer to these resources when making your own app.
When making your own app, ensure you use your own Vendor and App name. In this case you will need to change all instances of FrankL\Related to your own, unique code.
This app is fully functional and will be offered on the osCommerce App Marketplace when it goes live.
For now, you can upload this app to your catalog/includes/OSC/Apps directory in your osCommerce 2.4 installation.