Apache NetBeans
Free Apache IDE for Java and other languages.
AppOpen source
Open source IDE maintained by Apache, with support for Java, PHP, JavaScript and built-in Maven.
When to use
For Java projects with Maven or Gradle when you want a free, easy-to-install IDE.
When to avoid
If you need the broadest plugin ecosystem or deeper code analysis.
Alternatives
They do a similar job. Compare before choosing.
Classic open source IDE for Java, extensible through plugins.
AppOpen source★ 171IntelliJ, WebStorm, PyCharm: deep refactoring and analysis.
AppFreemium
Related
From the same area, with a close purpose.
Apple's official IDE for iOS and macOS.
AppFreeMicrosoft's full IDE for .NET and C++ on Windows.
AppFreemiumGoogle's official IDE for Android apps.
AppFree