What are custom controllers in Salesforce?

Custom controllers in Salesforce are Apex classes that allow developers to implement specific logic for Visualforce pages when standard controllers do not meet the application's needs. They provide a way to handle user interactions without relying on the built-in functionality of standard controllers, thus enabling more tailored control over the user interface and the data processing.

These controllers are coded to create custom behaviors, which means they can implement unique business logic, manipulate data beyond what is possible with standard controllers, and handle operations that are specific to the requirements of the page. For example, if there is a need to perform complex calculations or to manage user input in a unique way, a custom controller would be utilized.

Furthermore, custom controllers can be effectively employed to create interactive experiences like wizards or to perform HTTP callouts to external services. This flexibility allows developers to build seamless integrations and sophisticated user experiences tailored precisely to the needs of their organization.

Thus, the answer encompassing all aspects of custom controllers is correct, highlighting their comprehensive functionality and versatility within Salesforce development.