FreeFileSync is an interesting tool for comparing and synchronizing data (also with MTP devices), which is available under GNU/GPL license for users of Windows and Linux operating systems. The program is able to synchronize large amounts of data, containing files with a size of over 4 GB and very long names (even over 260 characters). It supports Unicode and also allows you to synchronize folder contents on the network.

All the algorithms implemented in FreeFileSync were written in C+++, with a very strong emphasis on optimizing their work efficiency. FreeFileSync, despite its simplicity of use, is equipped with many useful functions. It allows you to work in up to 4 modes:

automatic (changes are detected and applied on both sides), mirror mode (the right folder will be overwritten by the left content), update mode (copying new or updated files to the right side) and custom mode (allowing the user to define their own synchronization rules). Comparison of data can be done according to the size and date of modification of files and their contents. Of course, the user can synchronize the contents of folders without comparing them beforehand.

In addition to the basic functionality, the user is also provided with options that greatly facilitate the synchronization process. These include automatic backup removal when synchronizing large amounts of data, copying blocked files via Windows Volume Shadow Copy Service (Windows only), temporary file exclusion, file transfer privileges, a preview filter that allows you to preview the effects of work even before it is started, and an advanced synchronization lock mechanism that is useful when multiple users attempt to synchronize the same batch of data over a network. A great advantage of FreeFileSync is the ability to save the configuration of the program to external files, as well as to create batch files that allow you to perform synchronization at any time (just run the file) or if they are added to scheduled tasks in Windows, automatic synchronization of data on selected days and at a specified time.

The program is available in Polish language version. The installation file allows you to install on 32-bit and 64-bit systems. From its level you can also create a portable version of the application, which, after copying, for example, on a flash drive, will allow you to run the program on many computers without the need to install it.