1. A method comprising: receiving a call message specifying a type of application program to be called from a calling application program that is executing on a computer system; determining whether the computer system has any application programs of the specified type available for execution; if an application program of the specified type is available for execution on the computer system, performing the following: providing an application call message in a format recognized by a particular available application program of the specified type; and calling the particular available application program using the application call message.