bup is a program that backs things up.  bup has a few advantages over other
backup software:

It uses a rolling checksum algorithm (similar to rsync) to split large files
into chunks. The most useful result of this is you can backup huge virtual
machine (VM) disk images, databases, and XML files incrementally, even though
they're typically all in one huge file, and not use tons of disk space for
multiple versions.

It uses the packfile format from git (the open source version control system),
so you can access the stored data even if you don't like bup's user interface.

Unlike git, it writes packfiles directly (instead of having a separate garbage
collection/repacking stage) so it's fast even with gratuitously huge amounts of
data. bup's improved index formats also allow you to track far more filenames
than git (millions) and keep track of far more objects (hundreds or thousands of
gigabytes).

Data is "automagically" shared between incremental backups without having to
know which backup is based on which other one - even if the backups are made
from two different computers that don't even know about each other. You just
tell bup to back stuff up, and it saves only the minimum amount of data needed.