As an example, a folder action script might let me combine the Finder with any other application, such as, choosing completely at random, Sophos Anti-Virus:
set theScript to "/usr/bin/sweep -nc"
repeat with i from 1 to number of items in these_items
set thePath to POSIX path of item i of these_items
set theScript to theScript & space & thePath
set theScript to theScript & space & "--quarantine:mode=000"
do shell script theScript
end adding folder items to
that script then scans any file which appears in a particular folder and locks it if it contains a virus (up to a point). But that's not really the point, the point is that I haven't actually had to use any of the target apps in order to get this combined functionality. It's like I was able to summon the Megazord without having to actually talk to the individual Power Rangers. Erm, or something. And that, really, is how a computer should work; I didn't buy OmniFocus so that I could look at its icon, or a splash screen, I bought it because it can manage my lists of things to do. And I got iCal in order to manage events in time. If I have things to do at specific times, then I ought to be able to combine the two, and the computer can do the work involved. After all, that is why I bought the computer.