According to some sources, it can run over 750,000 Android Apps on Windows and Mac. But don't expect a lot because you'll meet some lag issues, especially when running graphic intensive apps. If you wonder if it has a Google Play Store too, unfortunately and fortunately, you need to download a launcher first (like GO Launcher EX on their built-in app market) to enable Google Play Store. But as what I've said, BlueStacks has a built-in app market where you can download Android applications. Well, for me, it's better to download a launcher if you want to have a full Android experience.
The software is free, you can download it on the official website of BlueStacks. Click here http://bluestacks.com.