btar
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Requirements for the program I imagine:

tar

duplicity libchop rsync dar btar btar some day
Should look simple enough Yes No (python) No (complex implementation) Yes No (own format) Yes (6660 C lines, can be unpacked with tar) Yes (could still be unpacked with tar)
Allows incremental backups GNU tar yes, with special index apart. Only with full files. Yes, with rolling checksum. Yes (content-based) Yes, but not multiple snapshots Yes, but only with full files Yes, using the index and optionally with librsync for big file deltas Yes, using the index and optionally with librsync for big file deltas
Verifiable integrity No data checksum No Yes (content-based) No (no checkums in the backup) Yes (but needs ciphering password in the host) Using filters, like signing Using filters, like signing
Allow ciphering or compressing Yes, any Some Some No (only zlib on transfer) Some (per file) Yes, any Yes, any
Easy remote incremental backups GNU tar yes, with special snapshot indexes Yes (with cache) Yes Yes (no snapshots) Yes, with its indexes Yes, passing the index Yes, passing the index
Indexed listing or retrieving No Yes (with cache) Yes Yes Yes Yes Yes
Serialisation (to a stream, from a stream) Yes No No? No No Yes Yes
Can use multicores No No Could be No No Only making the backup Yes
Resist partial data loss/manipulation. Only if not compressed No Index plays a major role. Then, there is the db. Yes Yes? Yes Yes
Redundancy No No No No No Yes (inter-block parity) Yes (inter-block parity)