is there a program (free, preferably) that can "update backup" various folders to an external HD? by "update backup" i mean it will copy onto the ext. HD but will not remove anything from it. say i used to have files A and B in a folder Z on my PB and made a backup in an ext. HD. since then, i erased files A and B, but created C on the PB. now, i want to backup folder Z in such a way so that C gets added onto the backup folder Z and Z will contain A, B and C... (note that if i simply dragged Z from PB to external, A and B will be lost because they aren't on PB anymore...) i found many choices in versiontracker - is there any that any of you guys recommend?