In 2011, a fundamentalist Christian radio network Family Radio paid for a series of billboards in the US and around the world, stating that Jesus Christ would return on May 21st, 2011. There was an associated website called "We Can Know," with a countdown clock. At the center of this madness was a man named Harold Camping.
While this may sound amusing, Camping's crusade for a faulty prediction caused real psychological and financial harm. The only reason Camping remains free from imprisonment for fraud is his religious privilege as a fundamentalist Christian leader.
In response to this media blitz, a Washington-state radio program, Ask an Atheist began a regular segment called "Countdown to Backpedaling" in anticipation of the response from Family Radio when the world failed to end. They also launched this site with a countdown clock counting to the day after the rapture, when the excuses would begin. For this, the show received international attention.
After that, Ask an Atheist wasn't sure what to do with the domain. So they've put a number of other clocks to other doomsday scenarios. It's always the end of the world somewhere.