Portlets are components that comply with the Java standard for portal components, as specified by the portlet specification, JSR 168. See http://jcp.org/aboutJava/communityprocess/review/jsr168/. ATG Portal fully supports the JSR 168 portlet standard. You can use the ATG Portlet Deployment Tool to take any portlet and deploy it in your ATG Portal application. The portlet will then function in just the same way as an ATG Portal gear.