First there is the one from Apple. It´s called "Dateien Abgleichen" in german, I don´t know the english name (maybe "Adjusting/Aligning Files"?). It´s free at my OS 9 CD as option to install (maybe also 8.6?).
Didn't Speed Doubler have a function that could be used to synchronize folders as well? I think when you copied a folder into a place where there was a folder with the same name, it added another choice to replace and cancel. Something like update to match or some such?