Category in Android

This indicates that activity is an optional operation on the data that the user is browsing.
Android. Intent. Category. Alternative

Activities that can be securely used by browsers must support this category
Android. Intent. Category. browsable

If the activity is an option that saves data (click, Center Press), you need to set this category
Android. Intent. Category. Default
 
Activity is a development preference panel)
Android. Intent. Category. development_preference

Can run in parent activity.
Android. Intent. Category. Embed

Used as a test instrument.Code
Android. Intent. Category. framework_instrumentation_test

This activity can be embedded in the host activity (activity that is hosting gadgets)
Android. Intent. Category. Gadget

Main Screen (activity), the first activity displayed after the device starts
Android. Intent. Category. Home
 
The activity should be displayed in the top-level launcher.
Android. Intent. Category. Launcher

Activity is a set Panel (preference panel)
Android. Intent. Category. Preference

Used as a sample code (not part of the normal user experience)
Android. Intent. Category. sample_code
 
Activity is an optional operation for user-selected data.
Android. Intent. Category. selected_alternative

Used for testing purposes, not part of normal user experience
Android. Intent. Category. Test

Should be used as a unit test (run through test harness)
Android. Intent. Category. unit_test

This activity can set wallpaper for devices
Android. Intent. Category. wallpape

This activity should be used as a tab in tabactivity.
Android. Intent. Category. Tab