System: Windows 10 Requitement: To synchronize specified files (docs, pics, music) on a removable USB drive with those of the main drive. Synchronization to be initiated manually, no need for continuous or automated sync. Ability to choose folders that will be synchronized, the choice to be remembered. Folders can include subsub...folders. Incremental propagation of additions, deletions and renames (if not incremental, it will take too long). Total size of files is considerable, so there should be no limitation in this respect requiring the Pro version. Any suggestions for a good free tool?