Email has had a good run as king of communications. But its reign is over.

In its place, a new generation of services is starting to take hold—services like Twitter and Facebook and countless others vying for a piece of the new world. And just as email did more than a decade ago, this shift promises to profoundly rewrite the way we communicate—in ways we can only begin to imagine.

We all still use email, of course. But email was better suited to the way we used to use the Internet—logging off and on, checking our messages in bursts. Now, we are always connected, whether we are sitting at a desk or on a mobile phone. The always-on connection, in turn, has created a host of new ways to communicate that are much faster than email, and more fun.