The popular flash game 'Diner Dash' from PlayFirst but in 3D and reimagined with Vocaloids.
Assign clients to a table and give them the menu.
Wait for them to decide and bring their order to the kitchen.
When the meal is prepared bring the food to the table.
When the clients have eaten their fill bring the check and clean the table afterwards.
Assigning clients to chairs with the same color gives them a boost.
If you let clients wait for too long they will leave angry and you won't get any money.