A removable card is adapted for insertion into a corresponding receptacle of a host device, and includes a processor for running at least one application. An agent program is downloadable from the removable card to the host device. The agent program runs on a processor of the host device and controls communication between the application running on the processor of the removable card and at least one application running on the processor of the host device. A different agent program may be downloaded from the card to the host device for each of the applications running on the removable card processor, and each such agent program controls communications between its corresponding removable card application and one or more application programming interfaces (APIs) of applications running on the host device processor.