Open source Dropbox software?
Take a look at the following.
Based on ghoti's comment.
The difference between cloud storage and remote backup is mostly buzzword, the number of remote hosts your backup is stored on and easy sync / use.
Other remote backup solutions that may meet your needs include
- unison also see automatic remote backups.
- rsync also see manual with ssh, rsync and lsyncd
- cron, ssh, and a version control system of your choice (git, sunbverstion, etc.) (cron job executing a commit command at a given interval, use postcommit hooks on the server to check for additional copies in others to use more than one host )
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