Answer: Briefcase

Long before there were syncing services like Dropbox (or, for that matter, long before there was a regular use of web-based apps and services in the first place), Microsoft had their own simple but effective syncing tool built right into Windows.

First appearing in Windows 95, the “Briefcase” was a special folder that supported simple two-way file synchronization. The premise was simple: put files and folders in the briefcase to mark them as files you wanted synced, then just right click on the briefcase and select “Update All” to sync the files when you were connected to an external hard drive, network drive, or whatever your syncing location was.

Though many readers will be surprised by this (because Microsoft downplayed the Briefcase functionality over time as cloud syncing rose to prominence), the Briefcase feature actually persisted well into Windows 8 (in a depreciated form) and was only totally removed in Windows 10—which means the old Briefcase had a solid 20 year run before it was retired.