Various classes in java.base define system properties.

java.time.zone.ZoneRulesProvider
java.time.zone.DefaultZoneRulesProvider
 
java.lang.ClassLoader
java.system.class.loader,java.class.path
 
java.net.URL
java.protocol.handler.pkgs
 
java.util.spi.LocaleServiceProvider
java.locale.providers
 
java.util.PropertyResourceBundle
java.util.PropertyResourceBundle.encoding
 
java.util.jar.Pack200
java.util.jar.Pack200.Packer, java.util.jar.Pack200.Unpacker
 
java.util.Currency
java.util.currency.data

java.util.logging.LogManager
java.util.logging.config.class, java.util.logging.config.file

java.util.logging.SimpleFormatter
java.util.logging.SimpleFormatter.format

The names of these properties are candidates to use the recently-new `{@systemProperty <name>}` tag, which will cause the property names to appear in the main javadoc search index.