Dropbox and Microsoft have announced the ability to co-edit Office Online files that are stored in Dropbox. With this, more than one person from a team can make edits and additions to documents without having to wait for the other person to finish what they are doing. Gone are the days of needing to send out multiple revisions because of edits that are requested, as co-workers can now just work alongside you on the document.
Source: ANDRIOD CENTRAL