zpaq is a journaling archiver optimized for user-level incremental backup of directory trees in Windows and *nix. It supports AES-256 encryption, 5 multi-threaded compression levels, and content-aware file fragment level deduplication. For backups it adds only files whose date has changed, and keeps both old and new versions. You can roll back the archive date to restore from old versions of the archive. The default compression level is faster than zip usually with better compression. zpaq uses a self-describing compressed format to allow for future improvements without breaking compatibility with older versions of the program.