A distributed, encrypted file backup system. https://github.com/ConceptPending/fincrypt Backups are verified at regular intervals to reduce the amount of trust needed in the system, and every file is stored multiple times. Eventually the goal is to attach a marketplace where end users will pay for the space they use and those who provide storage will get paid for doing so.
How do you solve the problem of an evil storage node provider who detects that you're trying to recover a file from backup, blocks it and sends you a "transfer X BTC to my account to get your data back" email?