Android is a Linux-based operating system designed primarily for touchscreen mobile devices such as smartphones and tablet computers, developed by Google in

conjunction with the Open Handset Alliance.Initially developed by Android Inc, whom Google financially backed and later purchased in 2005.
Google releases the Android code as open source, under the Apache License.Android has a large community of developers writing applications (“apps”) that extend the functionality of devices, written primarily in a customized version of Java.They are available for download through Google Play.

Short History
1. The first android phone was sold in 2008.
2. And by 2010 end android has become the world’s leading smartphone platform overtaking Symbian.
3. Android holds about 70% of the market share as per the latest results out.

Different android versions released
1. 1.5 cupcake
2. 1.6 donut
3. 2.0, 2.1 Eclair
4. 2.2 Froyo
5. 2.3.X Gingerbread
6. 3.X.X Honeycomb
7. 4.0.X IcreamSandwich
8. 4.1.X, 4.2 JellyBean

Please see the usage share of different version of android released, (Data courtsey : Wikipedia)