Android development starts with the Android SDK (Software Development Kit). While there are many different programming languages and a host of IDEs (Integrated Development Environments) you can ...

Google released the first public version of the Extension SDK, which aims to bring features of the latest Android version to older versions.

Now, in theory, the Android Open Source Project (AOSP) is still free and open source -- but the Android SDK is the de facto tool for developing apps for every flavor of Android.