In 2008, Microsoft acquired a start-up, Danger, that had built popular mobile phone software, hoping that technology would revitalize its waning phone software business. But Microsoft stumbled as it took longer than expected to create a new product with the technology. In April, Microsoft finally introduced the fruits of this labor when it unveiled the Kin phones. In contrast, Google, a chief Microsoft rival, also bought a mobile technology start-up — Android. Both Android and Danger were co-founded by Andy Rubin, who joined Google.