Many different applications have the ability to create a bootable backup. This entails copying all the files (including hidden files) on your hard disk to another volume while preserving Unix ownership, permissions, and symbolic links. Assuming you use the correct settings, such applications can also update a duplicate incrementally (rather than recopy every single file each time).
However, you should consider a few other things when looking at a duplication program:
Can it create a bootable duplicate directly onto a hard disk (as opposed to an intermediate disk image or optical media)? If you have an extra hard drive available, you'll want this capability.
Conversely, can it create a restorable duplicate onto optical media or a disk image? Sometimes this feature is useful, other times not.
Can it automatically update the duplicates on a schedule?
When updating a duplicate incrementally, can it also delete files that were deleted on the source volume? If not, your duplicate may include extraneous files that you don't want. (Of the software discussed here that offers both duplication and archiving features, only Personal Backup X lacks the ability to synchronize deletions when updating duplicates.)
Does it have any other features you might use, such as file and folder synchronization?
Retrospect Desktop vs. Retrospect Express
EMC Insignia's Retrospect software comes in several different editions, including Retrospect Desktop ($129) and Retrospect Express (bundled free with some external hard drives and optical drives; also available in a special software bundle from Allumesee Appendix C). The two applications are quite similar, the main differences being that Retrospect Express does not support tape drives or client-server backups and that its facility for selecting or excluding files is more primitive. You can find a list of differences, as well as the features of Retrospect's Workgroup and Server editions, at www.emcinsignia.com/en/products/mac_compare.dtml. One important issue not on that list: technical support. No matter which version you have, free support is limited to the FAQs, knowledgebase, and community forums on the EMC Web site. Paid support is available for both products, however; EMC charges $40 per incident for Retrospect Express and $70 per incident for Retrospect Desktop.
In this book, when I refer to "Retrospect" (without any other qualifiers), I mean that the features in question apply to all editions of the program. If a feature is applicable only to a particular edition, I specify "Retrospect Desktop" or "Retrospect Express."
The duplication programs I've tried are more alike than different, so if you're looking for an application to accomplish this one task, just about anything should do the trick. Joe's Software Recommendations, page 151, offers further advice.