Access your documents offline and edit them without being connected.
Platform: iPad, iPhone
License: Free for personal use only
A lot of people use Google Drive to store their Office documents. Surely then, all you'll need to view and edit these documents is the Google Drive app? However, Google have gone to the effort of releasing a lightweight, standalone app for doing the exact same thing.
Upon launching the Google Docs app, it also seems to provide identical functionality. Editing and sharing options are the same. One minor difference is that the Google Docs app is smaller and faster so those with tablets and phones that struggle with Google Drive may benefit. Aside from that, there's no seamingly obvious reason to choose Docs over Drive, especially as Google Drive supports spreadsheets and other documents in storage too.
The single most useful aspect over Google Drive is the fact it lets you access your documents offline, enabling you to both view and edit them without being connected.