OFBiz can be downloaded several ways. The easiest way for new users is to download a current nightly build as follows:
Trunk: http://ci.apache.org/projects/ofbiz/snapshots/ofbiz-trunk-current.zip
9.04: http://ci.apache.org/projects/ofbiz/snapshots/ofbiz-rel9.04-current.zip
Unzip the files in a directory of your choice. I use "/opt/ofbiz", but you may prefer "/usr/local/src/ofbiz" or something else. Windows users often use "c:\ofbiz".
Because the files are distributed in source code, they will work on any computer with a System Requirements#Java SDK, whether Windows, Mac, Linux, BSD, or others.