The Steam Page for Sid Meier's Civilization V - Gods and Kings now offers a playable demo for this expansion for Firaxis' turn-based strategy sequel (thanks Frans). There are no details on the demo, so it's not clear if this supports OS X, as the expansion and game itself offer SteamPlay Mac support. Here's word on the add-on:

Sid Meier's Civilization V: Gods and Kings is the first expansion pack for Civilization V - the critically acclaimed 2010 PC Game of the Year. This robust expansion covers the entire scope of time from founding your first Pantheon of the Gods and spreading religion across the world, to deploying your spies in enemy cities in order to steal information and technology.

As you move through the ages, you’ll interact with new types of city-states, engage in new city-state quests and global competitions, and master exciting new systems for land and naval combat. Civilization V: Gods and Kings will also include nine new civilizations, nine new wonders, three original scenarios, and dozens of new units, buildings, and techs that will offer even more ways for players to expand their empire and dominate the world.