

Yes, Syncthing needs 2 diferents devices to sync, FreeFileSync syncronize whatever you want within 1 device, for example between 2 Disks or from a network disk to your computer disk.
Syncthing works great if there are 2 devices turned on and connected to a LAN or Internet, and FreeFileSync is totally disconected from the internet and only needs 1 device on (the one that execute it)
I use both, Syncthing to autosync all my devices and FreeFileSync to backup all those files to various disconected hard drives
You should try LocalSend as an alternative to Airdrop with your Iphone friends!