A software (and optionally, hardware) project for automating the creation of offsite backups on flash drives. The idea is that you have a large-ish flash drive on your keyring; when you take your keys out of your pocket, plug the flash drive into the device. The specific use case is a hanging key holder with a RasPi inside of it. The files in the backup script are automatically encrypted and copied onto the flash drive. That way, if anything happens while you're out and about you have the latest and greatest copies of the files already with you.

Or, "You have LVM running on one box and an external drive, also running LVM, with the same volume group name - how in the hell do I mount the external drive?!"