AeroFS - File Sync Without Servers

Ultimate Privacy

AeroFS will only share your files with those who you invite. Files are never stored in the cloud unless you specifically enable Cloud Backup.

I just got beta access. It'll be interesting to see how it compares to dropbox. It'll be interesting to see how well it is able to sync to my other machines without a central server to pivot from. Since my computers tend to stay on, it may not be an issue.