Android is an open source operating system for smartphones and tablets, other than the iPhone and iPad. Its interface is mainly developed in Java, one of the most popular programming languages. One of the advantages of Android is the multitude of devices on which it runs unlike iOS that only runs on Apple supports. This feature can sometimes become a defect in the sense that, although officially compatible, some applications do not work on some terminals, because they have not been tested on all the - many - devices.