What might be the difference between "Zend Server Community Edition" and "Zend Server" with no licence (or an expired licence)?
My trial licence on my Zend Server has expired - so is that install now the same as the Community Edition?
Yes. Zend Server without a license (or with an expired license) is the same as Zend Server Community Edition.
"If you use Zend Server without a license (or if your license expires), you will still be able to use the basic product functionality, however features such as monitoring, diagnostics and updates will be disabled." http://www.zend.com/en/products/server/license