Let's say you are developing an application for a car dealer. Assuming that the car dealer sells many types of cars from different manufacturers. Each car manufacturer has many types of brands. For each brand, there are many models. The big question is: how do you deal with the interface for the user for this kind of hierarchical content?  

Chain selects can provide an intuitive interface for this kind of problem. Chain or dependent selects are html drop-down select boxes that are linked to each other. On the examples below, let's say you selected Toyota as manufacturer, brands under Toyota will automatically be displayed on the second drop-down. Selecting a particular brand will then display the models on the third drop-down for a particular brand.

ChainSelects makes it easier for you to generate these drop-down boxes. Install, configure, run and you're done! Fully working AJAX-based chained select boxes with minimal work.