Half of the world is celebrating something today, once-in-a-millennium combination the following will all occur on the 21st:
Purim, a Jewish festival celebrating the biblical book of Esther
Narouz, the Persian New Year, which is observed with Islamic elaboration in Iran and all the "stan" countries, as well as by Zoroastrians and Baha'is.
Eid Milad an Nabi, the Birth of the Prophet, which is celebrated by some but not all Sunni Muslims and, though officially beginning on Thursday, is often marked on Friday.
Small Holi, Hindu, an Indian festival of bonfires, to be followed on Saturday by Holi, a kind of Mardi Gras.
Magha Puja, a celebration of the Buddha's first group of followers, marked primarily in Thailand.