FreeFileSync is cross-platform software for syncing files and folders. It advertises as open source in many places, including multiple places on the project homepage, but their FAQ states:
Is FreeFileSync free for commercial use? No, the standard version of FreeFileSync is intended for private use only. The same applies to the FreeFileSync Donation Edition. Businesses and government institutions may still use FreeFileSync, but are required to buy the FreeFileSync Business Edition.
The project source is provided under a GPLv3 license, which does allow some additional terms to be applied by an author, but only specific types of terms which don't cover those reflected above, otherwise the license allows removal of such terms.
In a forum thread, the software author stated:
As the author and copyright owner it is my right to add exceptions to the GPL license as I see fit.
But as mentioned above these exceptions are in conflict with the license used. These "exceptions" also go against the commonly regarded open source definition. The advertisement of being open source, along with use of the GPLv3, while being advertised under these terms, could be considered misleading.
The licensing was directly queried in the project's forum here with no apparent official response.