Differ is an utility application for OS X compare the contents of two directories.
You can see easily and simply the comparison of the Xcode projects.
Why to use
We get a lot of benefit from version control system in Xcode. But it is quite hard to compare the entire project of both the old and new.
The difference between two revisions can be created by command line. This is not useful way to compare intuitively projects.
Differ simply presents comparison result of two directories by drag-and-dropping. It allows to compare projects without version control system.
And you can open files in FileMerge by double-clicking.