PC Backup (included in PC Tools 6, Central Point) notes
Central Point's PC Tools 6 includes PC Backup, which is notable for 1. Taking a very long time (over 90 seconds) to scan the hard disk for directories when it starts up on an 8088, and 2. totally making up for that by supporting the Central Point Option Board to speed up diskette format operations by nearly 50%. The interface was quite adequate, being easy to understand for most user levels.
PC Backup's "proprietary" format is similar to Norton Backup's format, except that instead of using 5 1024-byte sectors on 39 out of 40 tracks, it uses 10 512-byte sectors on every track of the disk. The amount of usable space is the same. Interestingly, it does not pretend to be a DOS disk at all and doesn't contain a "fake" directory with a message to the user (trying to read it returns "NON-DOS diskette"), but it does contain a boot block that prints out "This disk can't boot: it was formatted by PCBACKUP. Change Disks and Press a Key." if booted.
Central Point Backup (PC DOS 2000) notes
A pack-in with IBM PC DOS 2000, Central Point Backup's interface was the most functional and pretty. It was also slower than the others, which, combined with the generally lackluster file reading speed, made Central Point Backup the slowest program in the test. It is possible that this uneven speed contributed to the program taking longer with "save time" compression than "save disks (low)" compression (!).
Central Point Backup's "proprietary" format is similar to Norton Backup's format, except that instead of using 5 1024-byte sectors on 39 out of 40 tracks, it uses 10 512-byte sectors on every track of the disk. The amount of usable space is the same, as is the "Do not use this diskette" directory message.
While I had an Option Board in the test computer (see "PC Backup" above for why this is significant), support for it seems to have been removed in this PC DOS 2000 pack-in version.