TextureBox is one of several prototype games written during the design of Spore, that Maxis has made available for download.
From the Spore website:
The TextureBox prototype demonstrates the application of simple paint-program-style tools to dynamic cellular automata systems like Biome and CellCulture.
Use of Procedural Content Generation Methods
TextureBox implements an example of cellular automata which can be easily modified through a palette of tools similar to a paint program.