Platforms: iOS, Android (both free)
Google Drive is an essential cloud storage app if you use Google's productivity services, including Gmail, Docs, and Spreadsheets. You can not only store and sync important files across devices, but you can also create documents and spreadsheets from your tablet. Plus, you can share files easily with team members, who can edit the same document with you at the same time. No more passing printed drafts back and forth. On Windows 8? Access Google Drive in a browser.