Filer is an automatic file organizer. It takes the files it's opened with or that are dropped on it and moves, renames, copies or does all sorts of other things with them according to rules created by the user.
Filer is accompanied by AutoFiler. Instead of working on a set of files provided by the user, it can be started (automatically with Haiku) to monitor certain folders and deal with new files appearing there according to the user-defined rules.
For more information, see the accompanying documentation and rule making reference in the documentation folder.