Wicche

wicche /ˈwitʃ(ə)/ noun: A wielder of magic, caster of spells, practitioner of occult rituals; a diviner; also, a maker of magical potions or poisons. Gender neutral.

Wicche is a stand-alone spell casting system for your ttrpg.

You can follow along the development process here: https://joeyv.substack.com/