System properties for java 6 (System.getProperty("key") list of keys)

List of keys with  their description
(key = explanation

Key Description of Associated Value
java.version =  Java Runtime Environment version
java.vendor =  Java Runtime Environment vendor
java.vendor.url =  Java vendor URL
java.home =  Java installation directory
java.vm.specification.version =  Java Virtual Machine specification version
java.vm.specification.vendor =  Java Virtual Machine specification vendor
java.vm.specification.name =  Java Virtual Machine specification name
java.vm.version =  Java Virtual Machine implementation version
java.vm.vendor = Java Virtual Machine implementation vendor
java.vm.name = Java Virtual Machine implementation name
java.specification.version =  Java Runtime Environment specification version
java.specification.vendor =  Java Runtime Environment specification vendor
java.specification.name =  Java Runtime Environment specification name
java.class.version =  Java class format version number
java.class.path =  Java class path
java.library.path =  List of paths to search when loading libraries
java.io.tmpdir =  Default temp file path
java.compiler = Name of JIT compiler to use
java.ext.dirs =  Path of extension directory or directories
os.name = Operating system name
os.arch = Operating system architecture
os.version = Operating system version
file.separator = File separator ("/" on UNIX)
path.separator = Path separator (":" on UNIX)
line.separator =  Line separator ("\n" on UNIX)
user.name =  User's account name
user.home = User's home directory
user.dir = User's current working directory

source: oracle.com