You can track those and many more on the Interfaith Calendar, the generous work of a Methodist layman. The site not only shows holiday dates, but brief explanations of the parent religions.
You can find little-known holidays including St. Brighid of Kildare Day for Celtic Christians. You’ll also learn that Diwali or Deepavali is observed by three religions: Hindu, Sikh and Jain. A sizable glossary defines each holiday and its importance.
One page groups the major holidays by religion, although this would have been more useful if each holiday were cross-linked to the glossary. Another page groups religions by types: one god, many gods, no god, or some mixture.
You can even find out about newer, more exotic religions — like Cao Dai from Vietnam, the Middle Eastern Yezidis and Mandeans, even the alien-themed Raelian Church.
Another thoughtful touch: print-friendly versions of the list, usually keeping a month ahead.
Finally, there’s a list of sites on religion and food — not just practices like kosher, but even recipies. A tasty dessert for a nourishing site.