Preferences.app is, functionally, a clone of NeXTstep/OPENSTEP tool of
the same name. Just like the original program, it's a simple application
for setting preferences for the GNUstep system, with a friendly interface.
The program is simple, but powerful -- people can create new modules,
called "bundles", that add new things to the program that its original
developers did not think of or even intend -- that don't require
recompiling the main program. For more information on what bundles can do,
see StepWise. They are a very powerful tool.