Creator codes are four-character metadata which are attached to files by some applications to identify the application that created the file.
With previous versions of the Mac OS, when opening a file, files having a creator code would be opened using the corresponding application.
Starting with Mac OS X 10.6 (Snow Leopard), creator codes are no longer taken into account when opening a file. But with Magic Launch you can restore the original behavior for the file types of your choice.