UnDBX is a tool to extract, recover, and undelete email messages from Outlook Express .dbx files. On first run, all messages are extracted as individual .eml files. Subsequent runs only update the output directory with new messages, and delete old .eml files that correspond to deleted messages in the .dbx file. Corrupted .dbx files (including files larger than 2GB) can be opened in recovery mode, in order to recover messages and partially undelete deleted messages. The success of recovery depends on the type and level of .dbx file corruption.
Backshift is a deduplicating (variable-sized, content-based blocks), compressing (xz or bz2) backup program. Full saves and incrementals are pretty indistinct other than the amount of data transmitted, somewhat like with "rsync --link-dest" but without the huge number of hardlinks. It also de-duplicates large file content at a granularity of about 2 megabytes on average; there tends to be a unique copy of each file with size less than around 2 megabytes on average.