you can use oracle with anyone of them, but in general we use Oracle with large-scale business because oracle can manage database no matter how big it scale especially with the cluster option with oracle, and for the small business you can chose other RDBMS that can provide you the services and performance that you want with less costs compared to Oracle.
Oracle applications can be used on any scale of Companies. It has wide range of features and functions to cater the requirement of any kind of organization. Implementation depends on the company requirement and business operations and line of business and locations.
