Date: Dec. 31, 1997

Acquired for: $400 Million

Pushing to compete against Yahoo, the Redmond, Wash.-based software corporation invested in Hotmail and saw its acquisition become the largest web-based email service for over a decade. The move brought about an increase in email subscribers and web traffic, plus the integration of Microsoft web apps such as Windows Live Messenger and SkyDrive presented a fresh and innovative user experience unlike any other service at the time (besides Google). Microsoft recently discontinued Hotmail in favor of its new email portal: