Why: Talent, Technology
Probably the most accomplished of all the start-ups purchased by Yahoo! (save for Tumblr), Astrid was doing fine without an infusion of cash. Launched in 2008, it produced apps for all mobile platforms (iOS, Android, Windows) and had a good number of paying premium customers. Once acquired, however, the app was shut down and everyone given a refund. The app helped people stay organized by creating easy to-do lists and helping manage email. Don't be surprised to see some of its features wind up in a Yahoo! Mail app.