Those are only the files I consider important. Some definitions:
A mass is one of those objects you see on the screen.
The field is the array saving owner and height of all mass pixels, which correspond to screen pixels.
|main.c||main loop and framerate control|
|mass.h||the central, big mass struct (struct _Mass_)|
|mass.c||most of the engine, always experimental|
|field.h||struct _FieldPoint_ and globals concerning the masses alive|
|engine.h||parser for masses, particles, players, level specific settings|
|config.h||config file and command line parsing|
|video2d.c||SDL 2D stuff, drawing the masses and the debug HUD|
|video3d.c||same as video2d.c but for OpenGL|
|network.c||gathering player inputs, networking or loopback, replay files|
|mass-server.py||Mass game server|
|tests.c||make check, mostly tests for the wrapping helpers|