Parchive is a file format for redundant files. If any of the original files are damaged, the redundancy lets them be restored. It is used for transmission over faulty networks (like Usenet) and for protecting storage (like backups).
Version 2 clients had 7+ million downloads. Version 2 had bugs and limitations, so I’ve designed Version 3 with fixes and new features, such as incremental backups. Version 3 needs a reference implementation to be coded and tested.
It could be coded by a single person. The reference implementation just needs to read and write files and compute on the data. A follow on would be a high-performance implementation using threads, heavy optimization, and a static or dynamic library interface. It’s a good project for someone looking to prove their coding skills while doing the good deed of protecting data.