The only Arduino shield that can communicate with an Android device and provide many sensors and advanced features? Yes, it’s a thing now. 1Sheeld, actually.
From developers Integreight 1Sheeld blew its admittedly modest Kickstarter goal of $10k out of the water 8 times, but it’s now available to everyone from Amazon for $55. 1Sheeld is not intended to replace Arduino — it complements it by giving your Arduino projects access to the full set of smartphone sensor data and more. I can’t tell you about alternatives because there aren’t any.

design
No bigger than any other standard Arduino shield, 1Sheeld is based on the ATMEGA162 and includes a BlueTooth module on the bottom. The pin configuration is such that you will need Arduino Uno version 3 or newer (other Arduino models may vary, but anything newer than Uno rev3 should work). Each pin goes through so you can place additional shields on top, or use standard I/O pins as needed with adapter cables.
Two toggle switches are attached to the board. The first one chooses between 5V and 3.3V; 5v is the standard for use with most Arduinos, so if you’re not sure which one to use, use 5v.
The second switch, labeled UART SWITCH, will be in constant use; it switches between BlueTooth communication and Arduino programming mode. This is because it uses the same set of serial communication pins for both functions, but it’s not hard to figure out. If you find that sensor data is not being received, toggle it — it won’t break the board if you get it wrong.
3 micro LEDs show sending, receiving and BlueTooth status.
All in all, this is a very professionally made shield with solid solder joints and a well thought out design. White on black labels are crisp and easy to read, with no typos or misplacement.
Characteristics
By my count, there are currently 37 different «shields» that 1Sheeld can emulate. 11 of them are touch screens such as accelerometer, light, gyroscope, pressure. 10 more basic input/output operations such as: buzzer, keyboard, microphone, gamepad and various buttons. Another 7 manage communications and social networks: Twitter, Facebook, phone, email, Skype. Finally, there are 9 special function screens, including: voice recognition, speech synthesis, notifications, camera, LCD and data logger. You simply click on them in the app to add this functionality, although some will require additional configuration, such as Twitter authorization.
I think we can all agree that this is a phenomenal list of features — the sheer price of all these features from a single $55 purchase is pretty amazing (not including your phone, of course).