In December, 2011 USMLEWorld announced their iOS (iPhone, iPod & iPad) app to compete with their competitors. After a long wait, USMLEWorld announced their Android app on March 23, 2011.
The app is very similar to its iOS counterpart with having all the features of it and it works for all Qbanks provided by USMLEWorld (USMLE Step 1, Step 2 CK, and Step 3).
The app is available freely from Google Play here!