Revisions for Mac OS X lets you see all file edits in your Dropbox, and restore old versions of files and entire folders with the click of a button. In essence, this is “track changes” and “unlimited undo” functionality for your entire Dropbox.
Under the hood, Revisions relies on functionality already built into Dropbox: For all accounts (including free accounts), Dropbox stores all versions of all your files for the past 30 days. For paid accounts with the optional ‘packrat’ feature, and for business accounts, Dropbox stores your entire history, indefinitely. Revisions allows you to access and make use of all this data of yours in an intuitive way.
Using Revisions you can use Dropbox as a simple online backup solution, allowing you to restore old versions of your files in case you or somebody else makes a mistake that deletes or modifies your files.
Revisions allows you to use a variety of external apps to show the details of individual file edits: You may use Kaleidoscope, Changes, Araxis Merge, BBEdit, or TextWrangler to see changes made in any edit.
For more details, go to https://www.revisionsapp.com