There are several ways to detects where a Notes application is running depending what you want to detect.
@Platform - Detect the operating system where the application is running.
@ClientType - Are you application running in the Notes Client or on the webb. @ClientType will return Notes or Webb as a textstring.
@IsInCompositeApp - Running inside a composite application. returns True(1)/False(0)
@IsEmbeddedInsideWCT - Is the application running inside the Standard Notes Client it returns true or if it’s running inside the basic client then it returns False
@IsNotesBrowserPlugin - New in Notes 9 to check if your application is running in the browser plugin. It returns True if it does and if not it returns False
@GetMachineInfo - This @Formula was created to handle explicit policy selections but it can be using is ordinary applications also. The great thing is that you can use this to detect if the machine is a Laptop, get the ip adress, mac adress, available memory and alot more. Check out this support post
One thing to remember is that most of these functions is Notes client only.