Amazon S3 vs Rackspace Cloud Drive

Rackspace is known first of all as the top Amazon competitor on the Cloud Computing platforms market (Amazon Web Services vs Rackspace Cloud). But while Amazon continues developing its IaaS niche (Infrastructure for third-party web services), Rackspace decided to create its own Web services for the enterprise market. In May they launched Rackspace Email - hosted email server, and today they released Rackspace Cloud Drive - the enterprise file collaboration solution. Interesting that Rackspace also provides hosted Exchange and Sharepoint (that compete with its own services), but positions the own apps between the cheap but possible less robust Google Apps and the top-shelf Microsoft options.