Developed by a start-up in Bejing called SocketeQ, WindowsAndroid not only lets you mess with Android apps on your computer, but emulate an entire 4.0 ICS device on there, complete with all the settings and everything else. It's available for download from SocketeQ's site, if you'll give them your email address and—as you should be able to guess—it runs on Windows Vista, 7, and 8 exclusively.
WindowsAndroid will also make good use of the computer it's running on. It supports big resolutions, cranks up performance using your PC's guts, and can make use of your mouse and keyboard in addition to a touchscreen monitor if you have one. You can also side-load apps by dropping the .apks in the right folder. But for the moment, that's the only reliable way to get fun stuff on it, because Google Play doesn't recognize the hardware. More here.