In addition to Sun's JDKs (and their new Open Source Java project, see below), we know of the following Java or java-like implementations:

• Blackdown's SDK - a linux port of Sun's JDK (Info on license)
• GCJ and GNU Classpath - a free compiler and library for producing native binary or bytecode; compatibility unknown
• Kaffe (clean-room project, unknown compatibility)
• 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.

See also: JVM benchmarks in Volano Report

-- RoustemKarimov

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 (announcements, press releases, etc.)
• Open-Source Java Project Overview
• Free and Open Source Java - FAQ
• Open-Source JDK project community site
• OpenJDK SVN Access (code)