Public goods in general can vary in the extent of rivalyness and excludability. Let's think about a situation that happens a lot in school. Suppose three students get together and decide to work on a paper for a class. They break up the project into three parts and each works alone until they meet the day before the project is due (never a good idea!).
Analyze the quality of the final paper from a public goods' perspective. Do you think the optimal amount of the good be produced? Explain.