Nomenclature has been changed (pagesets rather than portals, etc) to avoid confusion, and datamodel/script name clashes, with the existing new-portal package. It can be run in parallel with .LRN/new-portal.
Client applications can build page layouts through the Tcl API, or can use the "extend package" facility of ACS Core to access a user interface that allows the management of pages and includelets similarly to .LRN.
For a complete (and useful) example of how to do so, see the documentation for the Layout Managed Subsite package, which provides seamless integration between ACS Subsite and the Layout Manager.