When developing applications for the Android platform, you have several choices of integrated development environment (IDE). The environments are free and easy to download on the web.
The best known IDE is the combination of Eclipse and the Android Development Tools (ADT) plugin. This option has been around for the longest. As the most mature option, this development environment has the best community support as well. Additionally, you have two options for installing this IDE. The first option is to download and use the Eclipse + ADT pre-configured development bundle. The second option is to download the Eclipse and ADT plugin separately. Either option works well, and you can find instructions for both on the Android developer site: http://developer.android.com/sdk/index.html
Netbeans also has Android support. The support is available as a set of NetBean plugins from a site called NBAndroid. NBAndroid provides a free basic plugin and a paid set of “extensions.” The extension include gradle support and visual layout editing for 15 euros.
Finally, Google andJetBrains have teamed up to create a new development option called Android Studio. The well-known IntelliJ editor forms the basic platform, and the companies have have tightly integrated the Android SDK tools. Android Studio is not final, but you can download a beta version from Google here: http://developer.android.com/sdk/installing/studio.html. Android Studio appears to be a tool branded under Google. However, you can get the same functionality from IntelliJ in either the IntelliJ IDEA Ultimate or IntelliJ IDEA Community Edition: http://www.jetbrains.com/idea/features/android.html
So, there you have it: 3 options for Android development that are available for free.