The App studio allows you to create visualisations which can be placed on the dashboard and profile. Apps can be as simple as an image or as complex as a technical analysis.
Apps are visual components which a user can add to their Hedgehogs.net public or private profile tabs or externally using some embeddable code (http://en.wikipedia.org/wiki/Web_widget). Think of an app as a small web page (which is actually what it is!). By combining apps from a variety of sources a user can thereby create a customized page representing their interests.
Apps can be defined by any user on Hedgehogs.net using the App studio. A degree of technical knowledge is required in order to define an app. You will either know how to write some HTML or have deeper knowledge of other web based visualization technologies such as Adobe Flash or Java.
You can get to the App studio reference guidehere. A full set of App studio tutorials starting with a 'Hello world' example ending with inter-app communication using publish/subscribe can be found here.