The first Underscore Backup pre-release is available for immediate download from Github.
- Public key based encryption allows continuously running backups that can only be read with a key not available on the server running the backup.
 - Pre-egress encryption means no proprietary data leaves your system in a format where it can be compromised as long as your private key is not compromised.
 - Runs entirely without a service component.
 - Designed from the ground up to manage very large backup sets with multiple TB of data and millions of file in a single repository.
 - Multi-platform support based on Java 8.
 - Low resource requirements, runs efficiently with only 128MB of heap memory.
 - Efficient storage of both large and small file with built in de-duplication of data.
 - Handles backing up large files with small changes in them efficiently.
 - Optional error correction to support unreliable storage destinations.
 - Encryption, error correction and destination IO are plugin based and easily extendable.
 - Currently supports local file and S3 for backup destinations.
 
Best of all it is available as open source for free under a GPLv3 license.
For now this software is still under heavy development and should not be relied upon to protect production data.