This webapp has three tabs. The first is a date diff calculator with some advanced features like counting the number of workdays beetween two dates, including Hungarian public holidays and Saturday workdays.
The second tab is a countdown timer. The timer can be shared with a link. Every browser with the same link is synchronized to the master timer.
The third tab helps you practicing the Doomsday algorithm and figuring out, which day is 21 December this year for example.