RubyDung

RubyDung was an unreleased strategy game created by Notch before Minecraft, developed until February 2009 at the earliest. Not much else is known about the game other than it was influenced by Dwarf Fortress, and that it was cancelled early in development, before it was even released. Notch's next game would be Minecraft (later known as Minecraft: Java Edition), which is based on RubyDung's codebase.

The name "RubyDung" was a placeholder name for a "dungeon game in the rubylands", the "rubylands" being a rough idea for a game world that Notch had. Rubylands is a project Notch was developing in early 2008.

About
While most gameplay features/mechanics are unknown - assuming there were any to begin with, as the game was cancelled during a pre-alpha state - the game was meant to be a clone of Dwarf Fortress had it been finished. It would be easier to play with a heavy focus on accessibility, unlike the former game which has been remarked for being quite complicated and unfriendly to beginners. Since the game was in an early development stage, no GUI, text, or any other such features appear in any of the existing screenshots of the game.

The game featured a 3D isometric perspective, as opposed to Dwarf Fortress's 2D tile-based graphics. It also included a 3d texture mapper, and randomly colored grass and cobblestone textures on the fly. The terrain generation was quite varied, containing many bumps, hills, and monoliths. Unlike the blocky nature of Minecraft, there appeared many sloped surfaces. There were trees present in the game too, for which there are lots of in the screenshots that they are present in. In earlier versions of the game, there was also a dirt material which formed maze-like dirt paths, and an alternate, earlier grass texture less resembling the one seen in Minecraft.

After the game was cancelled early in development, the codebase would later be reused for Minecraft. Even the grass block and cobblestone block textures that appear in later versions of the RubyDung would appear in the earliest builds of Minecraft.

Creation of Minecraft
RubyDung inspired Notch to make Minecraft when he wanted RubyDung to have a first-person view, but when he tried making this, he thought that the textures were too blurry and distorted. Shortly after Notch's days coding for RubyDung, he came across the game Infiniminer, which put down the foundations for Minecraft.

On October 30, 2009, Notch talked about RubyDung on his blog in an entry titled "The Origins of Minecraft".

Minecraft's source code came from RubyDung, as such, the earliest versions of Minecraft still internally refer to themselves as RubyDung, and still contain the terrain.png file from RubyDung, which dates to February 2009.