Android is based upon a modified version of the Linux kernel. It is a participant in the Open Handset Alliance. Unit sales for Android OS smartphones ranked first among all smartphone OS handsets sold in the U.S. in the second and third quarters of 2010, with a third quarter market share of 43.6%.
Android has a community of developers writing application programs ("apps") that extend the functionality of the devices. There are currently over 100,000 apps available for Android. Android Market is the online app store run by Google, though apps can be downloaded from third party sites.