A replicant is a "live view" that can be dragged out of an app and dropped onto the desktop (or into another app). Of the BeOS applications, only Clock and NetPositive use them. The Clock replicant (with its dragger) is shown here:
Draggers aren't displayed by default. To tell the system to display its draggers, choose Show Replicants in the Be Menu. Choose the item again (which will have since changed to Hide Replicants) to hide the draggers.
To get rid of a replicated view, drag the replicant to the Trash, or pop up the replicant context menu and choose Delete.