Beyond Compare 2 is an outstanding file and folder comparison software. It can be used for comparing and merging plain text, source code and binary files, as well as synchronizing local and networked folders. Although Beyond Compare supports a wide range of automatic functions, its main goal is to help the user analyze differences in detail, and carefully reconcile them.
Source: Beyond Compare 2 :: Diff Utils
Apart from what is stated, it’s an excellent folder comparison tool that I use to sync my internal and external backup drives.