A review aggregator is a system that collects reviews of products and services (such as films, books, video games, software, hardware and cars). This system stores the reviews and uses them for purposes such as supporting a website where users can view the reviews, selling information to third parties about consumer tendencies, and creating databases for companies to learn about their actual and potential customers. The system enables users to easily compare many different reviews of the same work. Many of these systems calculate an approximate average assessment, usually based on assigning a numeric value to each review related to its degree of positive rating of the work.