rusefi.com

6 DOF MPU-6050 Module 3 Axis Gyroscope+Accelerometer Module for under $2 usd.

http://www.ebay.com/itm/6DOF-MPU-6050-Module-3-Axis-Gyroscope-Accelerometer-Module-for-Arduino-MPU-6050-/272546609408?hash=item3f750b3900:g:-NwAAOSw44BYlyqp

"Based on the STM32F407VGT6, it includes an ST-LINK/V2 or ST-LINK/V2-A embedded debug tool, two ST MEMS digital accelerometers, a digital microphone, one audio DAC with integrated class D speaker driver, LEDs and push buttons and an USB OTG micro-AB connector."
(discovery datasheet)
btw. what is 9DOF in similar boards?

6 DOF means that based on gravity, you detect liner and rotation changes in X, Y and Z axis's.
https://en.wikipedia.org/wiki/Six_degrees_of_freedom

I guess 9 DOF might use a magnetometer, such that you add North, South, East, West degrees of freedom, or perhaps, pressure for elevation. Or perhaps it is used to describe a articulated robotic arm.

An accelerometer is typically a bit slow to react to changes when rolled on an axis, a Gyroscope allows fast reactions to axial rotation, but have a tendency to drift. An accelerometer with gyroscope allows for fast reactions to axial rotation, and the accelerometer prevents the longer term drift. This MPU-6050 simplifies the process of getting this kind of data and it does it for low $.