RubyDung (unreleased Minecraft precursor; mid-to-late 2000s)
RubyDung was a game created by Markus Persson (Notch) before his most popular game, the critically acclaimed Minecraft.
Originally influenced by the game Dwarf Fortress, the textures for the grass and cobblestone building blocks that were created for RubyDung were reused for Minecraft. Notably, some of the earlier, pre-classic builds of Minecraft were referred to internally as RubyDung, despite not actually being the game in question; this was before Minecraft was officially named.
For unknown reasons, Notch has never made the game public, except in screenshots from a blog entry on his Tumblr, called The Origins of Minecraft, which was published on October 30th, 2009. Not much else is known about this unreleased Minecraft precursor.