GateIn Portal interface is fully customizable using applications called Portlets. The Portlet API is described in JSR 286.

There are several technologies available for writing portlets. The most basic one is directly implementing the plain JSR 286 portlet interface. Alternatively, by means of JBoss Portlet Bridge, you can also use JavaServer Faces (JSF) and RichFaces for portlet development.

Whichever technology you choose, please refer to Starting a Portlet Project to learn how to set up your project in a robust and effective way using GateIn Portal Bill of Materials (BOM).