Tau Day, the counterpart to the idea of March 14 (3/14, as in 3.14) being Pi Day. The idea comes from “theoretical physicist” Michael Hartl who has a particular bugbear: he hates the idea of putting the emphasis on the ratio of circumference to diameter.
Something else that's special about today:
6/28 is the only day of the year where both the day of the month and the number of the month are perfect numbers: that is, a number that equals the total of the numbers it can be divided by, such as 1+2+3=6 or 1+2+4+7+14=28.
Hat Tip: Geeks are Sexy
Also, today is my birthday :-)