Applets provide a means of delivering a map-independent, mini-application without having to alter ArcPad's configuration. An important distinction to make is that an ArcPad applet is not the same as a Java applet, although it's similar in concept. An ArcPad applet is a small module that runs inside a full application—ArcPad.
Applets can contain toolbars, forms, and system object event handlers that access the ArcPad object model through scripts. Applets always have a .apa file extension, and can also consist of an associated .js,.vbs, or .py file containing JScript, VBScript, or Python code, respectively, that is called from within the applet.
Applets are created in ArcPad Studio and stored in ArcPad Extensible Markup Language (XML) format. Once the framework of an applet has been defined in ArcPad Studio, you can use any text or XML editor to make changes or additions. In fact, it's possible to create the entire applet using only a text or XML editor, although it's generally inefficient to do so.
ArcPad automatically loads applets after the default configuration has been loaded. Custom applets are usually placed in the Public Documents folder (that is, \\Public\Documents\ArcPad\Applets) but can also be located in the Applets folder under the ArcPad installation directory located in the Program Files area of Windows. You can specify additional applet folders on the Paths page of the ArcPad Options dialog box. To deploy an applet, simply place the .apa file (and associated .js or .vbs file, if present) in the system applets folder, the public documents applets folder, or a user-specified applets folder, and start ArcPad.