If for some reason your Android powered smartphone does not perform as good as it used to, or you want to sell it I suggest you to bring it to its original factory state.
This well kept secret surfaced just recently. All Apple devices running iOS 7 have a pretty darn well hidden Easter egg. Just follow this step-by-step instructions carefully and the very first Mac OS version 1 will appear on your iPhone or iPad. How freaking awesome is that?