- OpenJDK was originally developed by Sun Microsystems and later Oracle as an open-source implementation of Java. It became the reference implementation of Java 7 but Oracle only released official binaries once.
- Azul Systems develops and supports Zulu, a commercialized version of OpenJDK, to provide long-term support for Java SE 6, 7, and 8 as an alternative to Oracle's commercial support.
- Zulu is based on the open-source OpenJDK project but includes additional testing, packaging, and support. Azul contributes changes back to OpenJDK and provides Zulu freely as well as through commercial support contracts.