VaultSync
Sync directories and files in a secure folder on an external drive
...It is optimised to operate on a flash or external drive with minimal installation but it can also work on a hosted storage system like Dropbox, One Drive or Google Drive.
It is really important that a backup is simple and fast to make. There is no point in having to decide what files are important or what has changed at the time of the backup, or having to manually remove unimportant files from a deep folder hierarchy after a backup. VaultSync solves that problem.
Give it a try and send a review whether you like it or not. It can't improve without feedback.