Android is Open Source platform maintained by OHA (group of some mobile operators, software companies, chip developers). For instance some companies inside OHA are Samsung, Motorola, Nvidia and Google.
Android platform is open source and the software stock is available under Apache V2 Software license. So Android platform is free in other words.
There is $25 registration fee in case you would like to be Android developer and if you would like to publish Android apps to the Google Play—digital distribution platform for applications for the Android operating system.
Android is more like OS. It has the core apps: phone, camera, browser, calendar, settings; and it allows you to install different third party applications. The android app you may create can interact and integrate with core applications.