MEmu is a free Chinese application which runs Android in a window on your Windows desktop.
The main download is horribly slow, so we've linked to the main MEmu page, instead. This has more options, including a Google Drive download which is faster.
Once the download and setup is out of the way, life gets much easier. A window opens representing an Android tablet, a few basic apps - including ES File Explorer - and Google Play Store to help you find and add more.
A right-hand toolbar simulates shaking your virtual tablet, rotating it, adjusting volume, taking a screenshot, remapping keys or running an apk directly, while you can simulate multi-touch and tilting with the keyboard or a joystick.
The Settings dialog includes a "GPS Simulation" tab to define your location. It's set to China by default, so if you're elsewhere you should probably update it.
There are other settings to define the RAM allocated to the process, the number of CPUs, and the screen resolution (although you can run Android full-screen whenever you like).
MEmu also has shared folders for music, videos, pictures and download, making it easy to share content between Android and the host.
New installation package with overwrite install support
Switch to Android 4.4 as default and Android 5.1 is optional to download
Add widget tool, like cleanup memory, weather forecast, change wallpaper, etc.
Add message box
Add support to keymapping for MOBA game, like Penta Storm and Realm of Valor
Add support to keymapping pre-setting
Add support to customize tool bar
Add support to record audio
Improve the compatibility with Context3D games
Improve the compatibility with old AMD CPUs
Improve the graphic quality of unreal4 engine games
Improve the input method for some languages
Improve shortcut keys, like boss key
Update Google apps
Fix some tiny bugs
Installation and setup is awkward if you don't speak Chinese, but once you've got it running MEmu seems to be a reliable Android emulator, running all the apps we tried without difficulty.