Requirements documents are the game design of FreeOrion. "Published" documents are official and final, and guide (with varying precision) the game implementation.
Design document focus is primarily game mechanics in newer versions. UI design, art, audio and game content are generally not formally specified (though were more so in earlier revisions), but are instead discussed and refined separately and iteratively.
In-Progress Design Requirements
0.4 Design Pad - Deals mainly with ships and combat. Discussion on the forums is ongoing.
Published Requirements Documents
v.2 Requirements - Adds starlanes, planet environments and planet resource focus system
v.1 Requirements - Initial interface, galaxy setup and universe generation.
Roadmap - Provides a broad overview of FreeOrion's intended path to completion.