I'm looking for a Windows GUI program (preferably open source and/or free) to easily sync the contents of two USB-connected external hard drives, or a local directory with an external drive. Much to my surprise, this has proven to be much more difficult than it looks.
Synkron worked very well, but all of a sudden it stopped working (the main window does not open). I've decided to abandon it anyway as a new version has not been released since 2011.
FreeFileSync does not see all directories on one hard disk, for some reason.
rsync is command-line only.
Grsync is advertised on Wikipedia as existing also for Windows platforms but I was unable to find a Windows version.
Syncthing runs as a local service and is operated via a web GUI. Too bloated and complicated.