Description of problem:

Nautilus needs a mechanism to allow the user to add applications to
Open With... that appear regardless of file type. For example,
Nautilus will apparently only attempt to run a shell script. It should
also be easy to edit a shell script. emacs is an example of an
application that works with almost any file type. Opening a terminal
window in the current directory is another action that would be useful
to always be available.

When attempting to associate an application with a file, there seems
to be no awareness of the applications have been installed. The user
should not have to go find the executable for an installed application.

(nautilus doesn't seem to do anything with shell scripts. Perhaps it
is running the script, but that isn't apparent. I expect it to open a
window so that you can watch the script run. I thought the Ask Each
Time behavior preference would control this, but I guess not.)