GNU Classpath is a project aiming to create a free software implementation of the standard class library for the Java programming language. Despite the massive size of the library to be created, the majority of the task is already done, including Swing, CORBA, and other major parts. The Classpath developers have implemented almost all of the classes from J2SE 1.4 and 5.0. Classpath can thus be used to run popular Java-based software such as Vuze and Eclipse.
GNU Classpath has been one of the high priority directions of the GNU Project. While the source code of the "official" implementation from Sun Microsystems was available, the license did not allow distribution of any alterations. This was a major obstacle for many projects that could not progress without altering this code. The GNU Classpath development community includes institutions focused on research of Java virtual machines, as well as companies interested in providing alternative Java runtimes.
GNU Classpath is a part of the Free Software Foundation. It was originally developed in parallel with libgcj due to license incompatibilities, but later the two projects merged.
Read more about GNU Classpath: License, Uses, History, Development Team, Virtual Machine Integration, Support For The New Language Features in Java 1.5, Classes From The Omg.org Domain