On the informative blog Playing At The World blogger and game historian Jon Peterson has posted what is liklelythe earliest known variant of D&D: Rules To The Game of Dungeon. It's a retyping and partial scan of a set of rules written by the then teenaged author some 40 years ago with copious and informative notes by Peterson.
There are some quirky oddities in this rough relic of an age gone by. This is D&D as remembered and reworked by someone who played it (or one very much like it) in the earliest days of the game. This is a sampling of the cargo cult nature of early D&D back at the dawn of the RPG hobby.
A few curiosities of note: a dungeon adventure is called "The Descent" (how's that not totally cool?), magic-use is do-dad oriented where a spell caster buys (or fashions) the physical embodiment of spells. Priests can heal but lack the ability to turn the undead. Characters can have sons, daughters, or apprentices as heirs depending on class and chance. Levels start at a highly numbered rank and work down to 1 (for "1st class" I assume). Monsters have specific score certain weapon must get to harm the monster. The equipment list is quirky, humorous, and a little crazy.
If you like old D&D and want to take a look at how some folks did it back in the day go check out the blog entry for the pdf and discussion of a couple early adventures written for Rules To The Game of Dungeon. I myself really hope more of such materials comes to light as there were years of game playing, innovation, and interpretation that were and are little known outside small bands of players (if even outside a single backroom).