For specific needs, a user is not familiar with GIS and do not want to know how a GIS application can be generated, pragmatically, the user wants to perform on-screen map of the location he wants, can zoom in and zoom out, can display the location information and perform a simple query. To be able to meet it, a GIS Programmer will make a standalone GIS applications tailored to the needs of the user.

I've been playing around with the default from the ArcView Avenue Script 3.x to customize orders according to the end user. Later still there is a request to be made a standalone GIS applications, where the user does not want to know, how to make it and what is behind the application of GIS software later.
If you are still playing with Avenue The script, of course, have to play well with the legality of the software. But now there is an open source GIS software, which can be used as tools to customize so as to produce a standalone GIS application, which is free to use, not tied to the legality of the software. An example is MapWindow GIS Software. In addition to the Desktop as ArcView GIS 3.x, the MapWindow GIS ActiveX Control is also available MapWinGIS. By using this control, you can create your own version of your own GIS applications. Another example is gvSIG.
Desktop GIS Book blog in one of its news, shows how to create a GIS application you can make your own by using some Open Source GIS software follows:
QGIS 1.0
Qt 4.3 or higher and the development tools (Designer)
Python 2.3 or better