Mac users can now run Android apps on their desktop thanks to App Player from Bluestacks, an Android emulation platform that is available as an alpha version for OS X. Bluestacks does not specify any system requirements on its site, but in my tests App Player for Mac worked just fine on a MacBook running Mac OS X 10.6, Snow Leopard.
When you download and install App Player, the program sticks an Android apps folder in your dock for easy access. Clicking on any of the apps will start up the app emulator for you. If you're looking for the folder through the Finder you'll find it in Applications>Android Apps.
Right now, there are only 17 apps and games available for App Player on OS X such as Facebook, Glow Hockey, Paper Toss, Pulse, Seesmic, Twitter, Whatsapp, and Zebra Paint. Most of the apps run without many issues: Pulse responded quickly and was fairly easy to navigate, and the game Paper Toss worked well but was a little slow. I couldn't get Whatsapp, the cross-platform messaging service, to work, and I encountered the same problem when trying out Bluestacks' App Player on Windows.
App Player for Mac is pretty feature-bare compared to what Bluestacks offers on Windows, but that's to be expected since this is only an alpha release. You won't find any of the sync features the Windows version has, or the ability to download apps from the various Android app stores including Amazon Appstore for Android, Get Jar and Google Play.
Running Android apps on your Mac could be a handy feature just as it is for Windows users. At the moment, however, there isn't much content available to convince users to give App Player a try. Some of the 17 apps currently available such as Seesmic and Twitter are already available as native Mac apps, and you can find comparable games to what Bluestacks offers in the Mac App Store (although not for free). So unless you're dying to run Facebook for Android on your Mac, there's not a whole lot to win you over right now.
Nevertheless, Bluestacks says it will be adding new app developers every month, so keep your eye on App Player to see what new features and apps it adds over the next few months.
You can download App Player for Mac from the Bluestacks site.