|Why They're Hot:
With its on-site social and homework tools, college textbook seller and rental service Chegg.com keeps students coming back for more than just books. Its Homework Help tool lets students post questions to other students and educators when they are stuck on a thorny problem. Students can also start typing in a search box and immediately see what's already been answered on that topic from more than 2 million questions already asked and answered. The Homework Help tool evolved out of Chegg.com's acquisition of studying tool Cramster in late 2010. Students also assign ratings on Chegg.com to the courses they've taken. "Our goal," says Chegg.com CEO Dan Rosenweig, "is to connect students to educators and educational content to help them save time, save money and get smarter."