OpenJdk is an OpenSource FreeSoftware project based on source code released by SunMicrosystems.  Sun released most of the source code of its Java Platform Standard Edition, version 6 (though some was restricted by third parties.)  As of 2009, the Java community uses the Open''''''Jdk project to develop code that will satisfy the compatibility tests for version 7 of the Java Development Kit specs.  It has also developed an open source version of JDK 6, available for Linux and OpenSolaris.  

Open''''''Jdk contains source code for the HotSpotVm, a JavaLanguage compiler, and a suite of class libraries.

http://openjdk.java.net/

The Open''''''Jdk project also hosts closely related codes, such as the DavinciMachine project.