Lets try to figure out the requirements for the backend by writing down some user stories.
A user storie is a short and simple description of a feature told from the perspective of the person who desires the new capability.
It is as simple as: As a <type of user>, I want <goal/feature> so that <reason>.
Examples:
As a Cultris II player I want a highscore system so that I can compare my skill with others.
As a website visitor I want to see what this Cultris II is all about so that I can decide whether I want to play it.
These stories are rather abstract but they might help us to get started.
I suggest that we collect the Stories in the issue tracker