Android Studio is a free app for Android development.
Android studio is the official app designed to create android apps or to create specific tools wich can be helpful to edit or build an Android firmware.
Download links for Android studio:
There are also, many other applications for Android development.
However, this app (official google app for developers) is the most popular application for development purposes.
Compared to third party apps, this app is much more stable and updated regularly.
And most importantly, you can install this app on all operating systems such as Windows, Linux and Mac OS. However, the requirements for computer performance are higher.