Instagram is a free photo sharing service accessed through a mobile app that was launched in October 2010. Instagram allows users to take a photo, apply a filter, share it on a variety of social networking services, including Instagram's own social network.
Initially, Instagram was only released for Apple iOS devices. By April 2012, Instagram had garnered 30 million users. In April 2012 an Android version of Instagram was released. This caused some consternation among Apple devices owners who like the service being an Apple only social network. Some prominent Instagram users even announced that they were no longer going to use the service.
In less than four months on Android, Instagram has more than doubled it user base, now with 80 million users (Source: CNET). This case clearly a good move for Instagram and for Google is a demonstration of the reach of the Android ecosystem.