Oracle Application Express (Oracle APEX) is a development platform for building database driven applications with a modern web interface.
APEX apps can be developed quickly with a minimum of code. The out-the-box components provide a clean, responsive UI with the minimum of effort. Features can be added with small blocks of PL/SQL code or calls to database functions.
Here you will find guides and tutorials that can help you add those finishing touches to your apps. These are all methods I’ve found useful but may not have been obvious from the interface or Oracle help material.