Retrospect is a
backup/archival storage application originally developed for
MacOS, and extended several years ago to the the (32-bit)
Windows platform.
It's capable of local and network-based backups, supports virtually every kind of storage (from hard drives to floppies to CD-RW's to virtually every kind of tape drive and robot), and, in contrast with most other tools of its kind, has two very simple and easy to understand backup models: copy everything to tape, or just append what's changed since the last backup (this is known as an incremental backup). It's quite happy backing up Macs and Windows machines simultaneously.
Having shopped around over the years and sampled, almost literally, every other competing product on the market, from freebie throw-aways to $10,000 "storage solutions," I've found that this simple, quite cheap little program is an order of magnitude better than its next nearest competitor. When they support Linux my life as a sysadmin will be much, much easier.
My own experience with it is that it's extremely easy to use, well documented, well supported, and best of all, phenomenally stable. Having had some contact with the technical staff at the publisher, Dantz Development, I count them as rare in the commercial software world for their thorough approach to design and development, and their ability to produce quality code. If only the OS I ran the software on was this good. Five stars.