The Web UI is now a separate program from the core crawl-engine. They may now run in separate JVMs or even different machines, communicating via JMX. In the common case where you want one engine and one web UI, this can be acheived in a single JVM with command-line options.
The 'modules', 'submodules', and 'settings' job configuration pages are now rolled into the idea of a configuration 'sheet'. Alternate implementation modules are specified by going to 'details' from the sheet editor.
'Overrides' are achieved by creating additional sheets changing some settings/implementations, then associating those override sheets with certain SURT prefixes. For URIs of the given prefix, the alternate settings are used.