Basics

Game modes
There is only one "game mode" but you can greatly alter gameplay by installing mods. Aside from that the game itself can be altered from the game lobby which greatly influences gameplay.

Normal
Players start with 18 workers of their civilization.

Default
Players start with the map unrevealed (covered by fog of war) that they need to scout. Most Nations can develop Balloon at some point to reveal the map.

No Balloon
Players start with the map unrevealed and one can develop balloon.

Always Balloon
All Players see the map completely revealed from the beginning.

Default
Workers, civilian buildings and artillery can all be captured if not guarded by a military unit.

No Peasants
Same as default, but no capturing of workers.

No peasants, town halls
Same as no peasants, but town halls can also not be captured.

Cannons only
Only artillery can be captured.

No capturing
No unit or building can be captured.