Simple, secure cloud storage.
Even if some servers go down, your data is still safe and available.
Easy access to previous revisions of your data.
Users can be given read-only or read-write access to individual files. Files can also be made immutable.
Easy to use
If you are familiar with the command line and can write a cron job, you can use S4 for backups.
Application developers can use S4 for storage as well via its API!
What makes us different?
100% client-side encryption
Unlike all the widely-used, PRISM-compatible services out there, S4 does client-side encryption on every file. The server that stores your data can't spy on your files even if it tries!
Open source transparency
Unlike other client-side-encryption services, S4 is free, open source software. Anyone can read the code and confirm that it doesn't have secret backdoors; you don't have to just take our word for it.
— Jacob Applebaum, Tor Project developer and WikiLeaks volunteer
— Johannes Nix
— Comprehensive National Cybersecurity Initiative (CNCI), Report on National Cyber Leap Year Summit 2009
— Dr. Richard Stallman, president of the Free Software Foundation
— Tony Arcieri
— Geoffroy Couprie
— Patrick McDonald
— Pål Ruud