Greek oregano (Origanum vulgare) is closely related to, and similar to marjoram. It has a robust, stronger flavor than marjoram. Goes well with basil and a mixture of both is used in pizza and Italian pasta in the US. Used in Mediterranean cooking.
Mexican oregano (Lippia graveolens) is the traditional herb in Mexican cooking with citrus and earthy notes. A relative to lemon verbena, it pairs well with cumin, chiles and lime.