To create a Mac installer, first, build OpenSim:
  ./make-opensim.sh

Then open OpenSim.pmdoc in PackageMaker.  Delete OpenSim from the
contents pane on the left.  Then add your newly-built OpenSim folder
as new contents.

On the Configuration tab:
* Set destination to "/opt".
* Set Package Identifier to "com.opensimulator.opensim.pkg"
* Set version to the OpenSim version you built.
* Check "Require admin authentication"

On the Contents tab:
* Check "Include root in package"

Click "Build", save as "OpenSimulator-VERSION.mpkg".

To package it as a .dmg: (from http://www.wikihow.com/Make-a-DMG-File-on-a-Mac)
* Create a new folder, place the .mpkg file inside
* Right click the folder, select "Get Info", and note the size of its contents.
* Open Disk Utility
* Click the "New Image" icon to create a new disk image. Name it
  OpenSimulator-VERSION, set the volume name to OpenSimulator-VERSION
  as well, and select an adequate size (add about 9-10 MB over the
  .mpkg size).
* Copy the .mpkg file to the mounted dmg volume.
* Unmount/eject the .dmg.