XShelf is an application that enhances Drag and Drop operations in MacOS X by providing a shelf where drag-and-dropped items (such as files, text, or URLs) can be stored for later use. Thus, not only can Drag and Drop operations be "paused", multiple operations can be in flight at once. It is the spiritual heir to the NeXT Shelf.
iCommune is an application that extends Apple's iTunes to share music over the network. It allows you to share the music in your iTunes library and access other iCommune music collections. iCommune music collections appear as playlists in your iTunes window. You can browse through them, and choose to stream or download the music they contain.