RegisteredDomain is a simple library to extract the hostname from an URL in a consistent manner. It is based on the PHP version of the reg-dom-libs. The License is kept from the original, because the code hasn't changed much, except for making it PHP5.3 compatible, removing deprecated short-style PHP tags and replacing deprecated elements, and putting it under Composer package control.
I will try to keep it updated as new TLDs get added.