Sjogreen announced that 60 companies have had Timeline apps approved already, allowing Facebook to track all sorts of new things: when, where, and for how long a person using the RunKeeper mobile app went running, for example, or how long a person has spent reading a book on a Kobo e-reader. Until now, only a handful of Timeline apps were available, such as a music app from Spotify and news apps from Yahoo and the Washington Post. Many more apps will be created in the coming months, said Sjogreen.

Getting a much broader view of users' lives allows Facebook to offer a way for them to explore long-term trends, said Sjogreen: "We try to summarize all the activity [from an app] in a given month or year. It might show the places I've been, restaurants I've eaten at, whatever is most interesting or relevant."

Information that piles up fast, such as the songs a person has listened to, can be used to identify trends such as which songs defined a summer vacation, said Sjogreen. This feature is in place today. Summarizing the total distance a runner has covered, or which routes he or she ran most often, could help shape future workouts. "Summarization reveals patterns that can be really interesting," said Sjogreen. "We've just started with that, but there's a lot more we can do when we have more information."

The result will be a much truer representation of Facebook users' lives than the current profile page that lists a person's basic information, said Sjogreen. "You are more than where you went to college and who you married and your last five status updates, which is what the profile had been before."

Austin Haugen, a product manager for Facebook Platform, told Technology Review that Facebook was working on tools that could upload past activity from other apps and services to fill out a person's Timeline. He predicted that Facebook users and their friends would use the new Timeline to reminisce in extreme detail or to peek at the history of other users' lives. "I recently got engaged, and in 10 years we'll look back and say, 'Remember when we were planning our wedding?'" he said. "If we have a kid, they can use Timeline to see what was important to us back then."

Ben Silbermann, cofounder of Pinterest, a site where people create and share "virtual pinboards" of photos, products, and other content found across the Web, thinks this kind of tool is overdue. "Everyone's nostalgic—it's just that the Internet itself is really young," he says. "It takes a company like Facebook to start changing that."

Pinterest's Timeline app can show which of a person's online pinboards has been most active. Many people use them to organize ideas and inspiration for upcoming plans, such as a wedding or vacation, says Silbermann. Now Facebook will make it possible to look back at a significant event and see the brainstorming leading up to it.