zpaq is a journaling, incremental, deduplicating archiver for Windows and Linux. "Journaling" means that when you update a file or directory, both the old and new versions are saved. You can extract from the archive as it existed at any time in the past. "Incremental", means that when you back up your entire hard drive, for example:

zpaq -add e:backup.zpaq c:\*

that only those files whose last-modified date has changed since the previous backup are added. For 100 GB of files, this typically takes 1-2 minutes, vs. a few hours to create the first version. "Deduplicating" means that identical files or fragments are stored only once to save time and space.