DropScript is an app that you can drag a script onto to create a new application which invokes the script. The script can be any BSD-style script; it should specify its interpreter in the !# form on the first line, or /bin/sh will be assumed. Any interpreter on the system should work, such as sh, perl, tcl, etc.
The resulting app will past any "open file" requests it gets as command line arguments to the nested script. These requests are usually the result of dragging a file from the Finder onto the app's icon; they may also be the result of launching the app and then invoking the Open File menu item.
Source to DropScript is available via Darwin. See http://www.apple.com/darwin for more info. A copy of the source used for the Mac Hack demo is included, as well as the built program. DropScript must be installed in /System/Demos in order to work properly.
There are presently plenty of limitations in DropScript. See the file NOTES.rtf in the sources for more info.
There are two sample drop apps included. They are ShoveIt and UnShoveIt, which will respectively pack up and unpack documents. Files are gzip'ed; directories and archived in tar format and gzip'ed.
