Java SDK (Software Development Kit)
OFBiz is written in Java and requires the full Sun Java Development Kit (JDK) to run. It won't run on a Java Runtime Environment (JRE) alone.
Java version numbering is schizophrenic-- Java 6 means version 1.6, while Java 5 means version 1.5. Java version 1.5 is required for OFBiz release 9.04, while java version 1.6 is required for the OFBiz trunk.
You can get the latest Sun Java SDK here:
http://java.sun.com/javase/downloads/index.jsp
If Java is already installed on your target machine, make sure it is the full JDK and running version 6 (Build 1.6.*). You can chck this by typing "java -version" at a command prompt.
Java workalikes, including Blackdown, Kaffe, and others do NOT run OFBiz successfully (yet).
Operating system
OFBiz will run on any operating system that supports a Sun Java SDK. Microsoft Windows (XP and newer), Apple Macintosh (OS X and newer), Linux (most recent distributions), and Unix (FreeBSD, OpenBSD, NetBSD) are all supported.
Hardware
OFBiz can operate for evaluation and testing purposes on a minimal server. Current trunk installs take about 560MB of disk space. We have operated OFBiz on a 700MHz Celeron and 512MB of RAM running Debian Linux. Production servers will probably want more up-to-date hardware commensurate with the expected load.