Vulcan "mysticism" (TOS), the beliefs of Chakotay in the teachings of his ancestors (VGER), The Rules of Acquisition so that one could get into the Feringi version of Heaven (DS9), Klingons even believed in an afterlife! Kirk referred to the one who created us all. There are many "religions" perhaps more appropriately thought of as philosophies or belief systems in the Star Trek universe-but also the pervading belief that it was not right to impose one's beliefs upon others.