IntelliJ IDEA is an IDE, or Integrated Development Environment, by JetBrains. It attempts to integrate all of the development tools that you might need into one single place.
As per your requirements, you can download community or ultimate edition. As name suggests, community edition is absolutely free and we can use it for commercial development as well. Community Edition is free and open-source, licensed under Apache 2.0. It provides all the basic features for JVM and Android development.
However, ultimate edition is paid version and we can evaluate it freely for 30 days. It provides additional tools and features for web and enterprise development.
You can download IntelliJ IDEA from here. For detail follow steps in the video: