7. Twitter
Twitter
Free
www.twitter.com
Microblogging service Twitter was introduced in 2006, but it's come into its own this year. During the year that ended in October, the number of users posting short messages on the site grew sixfold, to more than 3 million. Companies of every size, including Best Buy (BBY), Comcast (CMCSA), and JetBlue (JBLU) began Twittering to provide customer support and advertise limited-time offers. During crises, like China's earthquakes in May and India's terrorist attacks in November, Twitter users tracked events minute by minute, sometimes unfolding more comprehensive and timely coverage than mainstream news outlets. And the site hit record levels of activity during election night on Nov. 4, when users were invited to share comments in a collective "Election 2008" page.
