On the mac forum it says warbirds 3 is free but it's a mmo where you pay a monthly fee.
http://www.insidemacgames.com/forum/...howtopic=31246
Edit: The fee is for playing online. But you can play it offline as well.
http://www.totalsims.com/
BTW thanks for finding this I am a mac user as well it sucks that there is nothing really out there for us.