OpenJDK 21 is an open - source implementation of the Java Platform Standard Edition. It is developed through a collaborative, community - driven process. It offers a comprehensive set of libraries and tools that enable developers to write, compile, and run Java applications. With its open - source nature, it encourages innovation and customization, making it a popular choice for a wide range of Java - based projects, from small - scale applications to large - scale enterprise systems. It also provides a high - level of compatibility with other Java - related technologies and adheres to the latest Java standards.