Google began developing Android as an open source operating system for mobile devices. In 2005, Google acquired Android and launched the Open Handset Alliance in 2007 with many industry partners. Android was the first open and free mobile OS, allowing developers to easily create apps. Google invested heavily in Android due to the growing mobile market and opportunity for targeted mobile ads. For Android to be successful, it needed to gain significant market share from Symbian and remove Nokia as the leader. While Apple and Nokia posed threats, Google worked with OHA partners to develop smartphones that could compete. However, it would be difficult for any single mobile OS to become a "winner takes all" due to differentiated features across platforms.