Does a basic/research RTS engine/model exist that can be used as a basis for further experimentation/research? I'd like to avoid reinventing the wheel if possible.
I'm aware of Spring Engine and Stratagus, but those are real game engines and may not be the best to experiment with and learn from.
Ideally the docs for the model would answer questions like:

• How exactly do units move? (constant velocity? constant acceleration? constant force?)
• How is pathfinding handled? Does every grid cell become an A* graph node (may be expensive)? Does it consider threats?
• How are groups handled? (w.r.t pathfinding and movement)
• How is combat handled?

I'm mostly interested in the low-level model details (for now), not the graphics etc.
I've read a lot of the other quesions (and answers/references) tagged RTS but I haven't found my answer yet.