Very good sync tool between different folders and operating systems.
Simply, THE BEST ONE ! - You only need this incredible program in order to analyse two folders, see the differences, and update one by the other. It compares and display even binary differences if you want. Sometimes you think your files are equal by the size, name, etc, but it is always good to compare your backups binary, in order to see if everything is ok. With FreeFileSync you can. Excellent.
Very good !
Best Free File Compare Tool
One of the few diff tools that works with more than just text and image files, Araxis Merge lets you also compare office documents (like MS Word, Excel, Powerpoint, or ODF). For people working on both Windows and Mac, it's great to know that a single license is valid for both platforms. The Beyond Compare team makes a fine diff tool for Windows (as well as Mac and Linux, by the way). It goes well beyond (pun intended) diffing simple text and also allows comparing PDF, Excel and image files.