Add "file group" multiple file handling capability.
A nice interface for creating file groups.
A file group, as viewed by visitors.
File groups have tags and these are used to "relate" file groups to posts. A "related file groups" widget and "upload related file group here" widget are included.
Files in your WordPress installation not attached to file groups ("orphans") can be easily turned into their own file groups. See the "Migration" section of the readme for details.