Summary: Despite the description saying "Mac OS X 10.5.8 or higher" this does not work with the latest OS X version, Yosemite. You get this error message: "You can’t use this version of the application “Civilization IV” with this version of OS X." and it is documented elsewhere on the web. I should have done more research. Furthermore, I don't see how to "return" online downloads, so I guess I just wasted a few bucks. Oh well, I hope someone else sees this before they download.
Summary: Apparently this download will not work on the new Yosemite for Mac. So money wasted... Don't download and please let me know if I missed something. I contacted Aspyr and their site stated this version is not compatible with Yosemite and they have no patch in the works. Wasted money.
Summary: This will not work on OS 10.10.1 and Aspyr is fully aware of the problem though they make no mention of it here. When you visit their support page you will find that buying it here gives you a version that will not work with the latest operating system.
Summary: Don't buy this. Unless you bought Civ 4 from Stream. Stream does not recognize Civ 4 unless you bought it from them. And there is no way for stream to help you. They just send you to their community help page. I should have a least put on some make up because I like to look pretty before I am screwed.
Summary: This does not work if you had Civ IV from before the 'Steam' or whatever the platform is. A waste of $10. Do not buy unless you bought civ from 'Steam'. It is not possible to register your older copy on the poor quality 'Steam' app.