- Free version is probably what you want, if you never tried Wormkout before.
- Paid version same as free, but without ads. Price is less than two dollars.
- Demo version is intended for testing new features.
At this point (September 2014), Wormkout is only available for android devices (version 4.0.4 and higher) which have required sensors – accelerometer, gyroscope and magnetometer (without them it would be kinda hard to track your movement).
Here is slowly growing list of compatible devices, so you can check whether your device is compatible before you go further.