Apple have already got experience for a Graphical User Interface. Their Apple Lisa was released in January 19, 1983 with it's own OS which have GUI. Lisa OS is a first GUI OS that is marketed alongside with it's PC. It costed $10k, and units sold also 10k, But it is so expensive, compairing to IBM XT that costs $5000. Lisa OS have most things, that Mac OS will have. Apple modified Lisa computer into Macintosh XL with System 1.1 to 3.1, and even added MacWorks Plus II to support up to Mac OS 7.5.5! Now that's you should call it a support!

Apple releases the personal computer 'Macintosh', with it's Mac System Software on January 24, 1984. On current age that would be nicknamed System 1. It would reintroduce Menu bar with it's Apple logo "menu" button (that was @ in prototypes", File (basically about the file), Edit, View, Special (that's how you shut down this computer), and more menus for every applications. They are in a top of the screen in default, instead of a window in Windows.

"Special? It's special to turn off your computer?" - Marhly, Reactor in FBE React team

Another thing is a Desk accesories. They are a fathers of Widgets on your Windows Vista/7, Mac OS X, and the history is silent about Desk Accesory precedors, if any of these are existed. It had next of these DA's:

Alarm Clock — This DA could be used just like an alarm clock, as the computer would beep, and the menu bar would flash when the alarm's set time was reached. It could also be used as an easier way to change/set the time and date on the computer. When opened, it would show the time and date set on the computer.
Calculator — A basic calculator capable of addition, subtraction, multiplication, and division. It featured the basic 10 buttons for input.
Control Panel — The control panel was used to adjust some of the settings on the computer. What made the original control panel unique from other Mac OS control panels was the intended absence of any text. This was chosen to demonstrate the graphical user interface. Representation was achieved by using symbols. It could be used to adjust settings such as volume, double click speed, mouse sensitivity, and desktop background. On the Macintosh 128K, Macintosh 512K, and the Macintosh Plus, the screen brightness was controlled by a mechanical adjustment wheel beneath the screen.
Key Caps — A DA used to show the layout of the original Macintosh keyboard. It did not show what happened when normal keys were pressed along with special characters (Command, Shift, Option).
Note Pad — A note taking DA that would save text entered into it on the floppy disk. Multiple note pages could be written when using the folded corner symbol in the bottom left corner of the note page.
Puzzle — A basic 1-15 slide puzzle, similar to the picture puzzle found in later versions of the Mac OS.
Scrapbook — This DA was similar to a cut, copy, and paste library. In it, one could store text selections and photos which could then be transferred to other applications.

Also, it have Macintosh File System just for 400 kilobytes of floppy disk.

In Mac build 16D0 (July 1983), Floppy disk icon was their desktop.

In early prototype, on August, there was a FREAKOUT.TXT, which containes a f-word. (something was overhauled to make Macintosh Word Processor work better, and is now totally fucked up, they said)

In late protoype, there is already the Apple logo as a menu, but it have Steve Jobs' face as a SYSTEM file, naked mac user as a Starter and The Gallery, Coke as a Reversi, A man on a hypnosis as a Finder. Also, there is a personal messages for a finder dated in October 1983, and created by Bruce

They had fun while working hard, but they did ended up releasing the revolutional operating system at terms of 1984 (the RTM build was builded on January 18, 1984, thought.)