Installers for Mac / Linux?

[Levi Kendall]

Hi all,

  I am preparing to release a stand alone application and am working
on doing Mac and Linux distributions along with Windows.  As far as an
installer for these, I am planning on using the Nullsoft install
system for Windows because I am already familiar with it and it has
worked great in the past.  My question is what should I use to package
the Mac and Linux?  Is there any Windows software that could be used
to make installers for Mac or Linux?  I currently do not have a Mac or
Linux machine to use for this, so it will be difficult if the
installer needs to be built on the platform it will be used to install
on.  Any tips?

-Levi