Best for five minutes.
For the inter-meeting gap or the elevator ride, the highest-impact destinations are:
Pointer Pointer — move your cursor anywhere, a photo of a person pointing at exactly that spot appears within two seconds. The whole site is the joke.
The Bored Button — a single big red button. Each press launches a different micro-game. Useful when you can't be bothered to pick.
Find The Invisible Cow — your speakers say "cow" louder as you move toward where the invisible cow is hidden. Three minutes of confusion, a small triumph at the end.
Cat Bounce — cat GIFs that fall, jump, and bounce when clicked. Fifteen seconds of work for ninety seconds of laughter.
Eelslap — hold your mouse button down to make a fish slap a man's face on a loop. Funnier than it sounds. We don't make the rules.
For more in this register, the Useless Websites and Optical Illusions categories are where to browse.