The last time I opened Extras there was a Content Management System that is now not available
This could be due to several reasons. Please check your Internet connection. If it is not working MAMP PRO will use only show Extras that you have previously installed. An Extra will be missing if the PHP version a host uses does not meet the requirements of an Extra. Do you have enough free disk space available? Some Extras can only be installed once per host. e.g. webEdition.