Edit:_ .dmg on Mac.

@purplecabbage has suggested using Inno for creating a Windows installer.

Possible solutions for creating Mac installers:

http://sourceforge.net/projects/macinstallerapp/
http://www.macupdate.com/app/mac/34613/packages

For creating DMG file:

http://www.wikihow.com/Make-a-DMG-File-on-a-Mac
https://github.com/andreyvit/yoursway-create-dmg

Yesterday, I had the opportunity to chat with @jahoni about the installer experience on OS X. From our chat, she had a few questions that I've looked into and I'll summarize here:

Show me two good examples

Evernote

Dropbox

What is the standard window size of a mounted image (.dmg)?

As far as I've found, Apple does not encourage a standard size. Both Dropbox and Evernote use custom sizes.

I created a default DMG using the Apple Disk Utility. When I found the image, the window size is 1540x810 (retina) or 770x405 (non-retina). Here is what it looks like:

Can the window resize be disabled?

No, the mounted image opens a Finder window that cannot be locked down in any way.

As you can see, the user can resize the window however they wish:

Tell me about the background image.

The mounted image is simply a customized Finder window. You can mount any DMG (Evernote or Dropbox for example), open the window, and click View -> Show View Options to see the customizable properties.

The background image is very limited. You can define an image, but you cannot define how it is displayed (tiled, stretched, etc) or the image resolution. The image resolution is particularly important. I've recently noticed that all DMG installers have non-retina background images - I believe this is because the image dimensions cannot be specified and a non-retina image must be used to look proper on non-retina displays.

It's safer to use a flat color.

Tell me about the icons

You can position and size the icons, but the user can always change that. Each mounted image has a slider in the top-right corner. This allows the user to scale the icons. This can also result is strange rendering issues when you are creative with the background - for example, checkout what happens with Evernote icon glow:

Can we show a EULA?

Yes, it looks as though we can define the text to shown. The EULA will be shown before the image is mounted and the user must agree to it:

Inno Setup sample code to disable Windows firewall prompt.

@mwbrooks - thanks for looking into all those specifics. I'm partial to the visual design and content of the Evernote example.

Let I need to step in to create the visual assets, or if @GarthDB will be taking the reins.