In Catholic Christianity, today is the Feast Day of Saint Francis of Assisi. He died the evening before, in 1226, two years after he received the stigmata. A feast day in honor of Francis' stigmata is celebrated on September 17, although some liturgical calendars omit that day as being close in observance and meaning to St. Francis Day. Francis was, of course, an Italian preacher and friar who founded the Franciscans and the Franciscan Clarist Order. Because of his association with nature and creation, many churches, including Protestant congregations, have "blessing of the animals" components during Sunday services on or near October 4.
Today is also Hoshanah Rabbah in Judaism. It is the seventh day of the Sukkot festival and is considered the last of the Days of Judgment that began on Rosh Hashana. The judgment for the new year is sealed on Yom Kippur but not delivered until Hoshana Rabbah. This site and this site provide more information.
In many Christian denominations, this is World Communion Sunday. Happening on the first Sunday of each October, the day originated in the Presbyterian denomination in the 1930s and was endorsed and promoted by the Federal Council of Churches (now the National Council of Churches) in 1940. The day promotes ecumenical cooperation and Christian unity.