Freeciv has been a very attractive alternative to Civ2 for years, but it had problems with its AI for a long time (their only AI programmer had produced absolutely unintelligible code and then vanished, so the AI couldn't be improved because no one could understand the coding). There also wasn't much of diplomacy possible with AIs, due to the same reason. I stopped following FreeCiv development a long time ago though, so it's possible that they found a way to solve this problem in the meantime. If they have, then I'd definitely recommend FreeCiv over Civ2.