In addition to [Sun's JDKs|http://java.sun.com/] (and their new ''Open Source Java'' project, see below), we know of the following Java or java-like implementations:

* [Blackdown's SDK|http://www.blackdown.org/] - a linux port of Sun's JDK ([Info on license| http://www.blackdown.org/java-linux/docs/support/faq-release/FAQ-java-linux-8.html#blackdown-scsl-position])
* [GCJ|http://gcc.gnu.org/java/] and [GNU Classpath|http://www.gnu.org/software/classpath/] - a free compiler and library for producing native binary or bytecode; compatibility unknown
* [Kaffe|http://www.kaffe.org/] (clean-room project, unknown compatibility)
* [Japhar|http://www.hungry.com/old-hungry/products/japhar/] (clean-room project, unknown compatibility; no change since 1998)

[ebu] - This was the result of a quick survey, short of facts. Feel free to update and amend.

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See also: JVM benchmarks in [Volano Report|http://www.volano.com/report/index.html] 

-- [RoustemKarimov]

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!! Open Source Java

Sun is now seeding open-source communities around its implementations of the Java platform. The company is releasing the code under an open-source license, and putting in place the infrastructure for a community to collaborate on a source-code commons.  Already released components includes the ~HotSpot Virtual Machine and Java programming-language compiler (javac), with complete NetBeans project metadata, with the remainder of the open-source JDK to be made available in the first half of 2007.

* [Free and Open Source Java| http://www.sun.com/software/opensource/java/] (announcements, press releases, etc.)
* [Open-Source Java Project Overview| http://www.sun.com/software/opensource/java/project_overview.jsp]
* [Free and Open Source Java - FAQ | http://www.sun.com/software/opensource/java/faq.jsp]
* [Open-Source JDK project community site| https://openjdk.dev.java.net/]
* [OpenJDK SVN Access (code)| https://openjdk.dev.java.net/source/browse/openjdk/]