For our NITRC project, which is based on GForge 4.5.x, we wanted to integrate it with MediaWiki.  However, while the latest version of MediaWiki (which has group workspaces) runs on PHP 5, and all of the GForge documentation refers to a PHP 4 dependency.  So, I simply tried to upgrade, and it worked!  There was only one change that needed to be made, in /etc/php.ini set:

allow_call_time_pass_reference = True

Since allow_call_time_pass_reference is deprecated, eventually we’ll have to worry about it if we keep upgrading our PHP, but for now we can stick with the latest PHP version.