Idea

How about making an application for portable devices, on which the user should be able to install any sub-application of his choice, so that he can just plug-in the device and the sub-application starts running?

E.g. Say we make an application of our own called "Jobless". We should be able to install Firefox, Winamp etc... on it, so that the user can just plug-in the device on any computer and start using the softwares of his choice.