@Matt_H:
To get AI player in Freeciv enter the following into the server before starting a game:
set aifill x
where 'x' is a number up to 30.
IMO Freeciv blows Civ and CivAGA out of the water, even without all features yet implemented.
It does take a bit of effort to get it set up, but if anyone needs help just ask me.
I spend way to much of my time playing/modding that game.
It is multiplayer but you need two computers and some sort of network or link. Or you can play on-line over the pubserver.