The answer to WHAT is simple. Ticktockonline.com is a website which displays how much time's left today, rather than how much has passed.
More important than WHAT is WHY.
Maybe inherited from our ancestors, our clocks display time from 00:00:00 to 23:59:59 by adding second. That brings me an illusion of gaining another day when the day ends! If your reaction to the illusion is, "what the hell are you talking about? in what universe you gain a day when it ends", welcome to join me! That makes two of us. When time keeps flying, our life gets shorter and shorter rather than "gained another day". What a cruel fact it is!
To remind me of the cruel fact, I decide to build this website (browser extension and app is coming soon). By watching the gidits become smaller and smaller, it urges me to make better use of the rest of my life.
If you are also interested in this, please feel free to email me your idea ( i#ticktockonline.com # -> @). An update email will be sent to you when there're something new released if you've subscribed.