S4 is described as '= Simple Secure Storage Service. S4 is Least Authority's secure off-site backup system for individuals and businesses' and is an app in the backup & sync category. There are more than 25 alternatives to S4 for a variety of platforms, including Mac, Windows, Linux, Web-based and Android apps. The best S4 alternative is Nextcloud, which is both free and Open Source. Other great apps like S4 are Duplicati, ownCloud, IPFS and Seafile.
On-premises solution offering file sync, universal data access and collaboration through Nextcloud Files, Talk, and Groupware. Ensures secure, controlled data storage for enterprise with powerful privacy tools including encryption, fine-grained access, and a bug bounty.
Duplicati stores encrypted, incremental backups with AES-256 encryption and GPG, compatible with Windows, Linux, MacOS. Supports cloud services like OneDrive, Google Drive, and includes a built-in scheduler, auto-updater. Run backups through a web interface or command line.
Self-hosted option for secure file sync, sharing, calendars, contacts, and mail supporting mobile, desktop, web access and external storage, real-time collaboration, password-protected links, document editing, anti-virus scanning, and LDAP integration.
IPFS is a global, versioned, peer-to-peer filesystem. It combines ideas from Git, BitTorrent, Kademlia, SFS, and the web. It is like a single bittorrent swarm, exchanging git objects. IPFS provides an interface as simple as the HTTP web, but with permanence built in.
Open source cloud platform for organizations with self-hosting, device file synchronization, sharing, versioning, secure encrypted storage, admin controls, web access, audit logging, and support for desktop and mobile clients for secure collaboration.
Seafile is more similar to Dropbox than to S4. It's a sync service hosted in Germany (Seafile.de) and uses an open source client (Seafile.com). S4 is a backup service only. They promise a sync folder but that's not yet available.
SpiderOak provides an easy, secure and consolidated online backup, storage, access, sharing & sync tool for Windows, macOS, and Linux (Ubuntu, Debian & Fedora). SpiderOak offers a different approach to online backup, synchronization, and sharing.
Spideroak is end-to-end encrypted (zero knowledge), like S4. It is cheaper and offers a Sync folder (S4 are planning one). However, with SpiderOak you don't get unlimited storage, which S4 does offer.
End-to-end encrypted file synchronization and sharing on desktop and mobile, featuring admin controls, auditing, link-based sharing, two-factor authentication, offline access, granular permission management, and protection for sensitive workplace documents.
Pioneering scalable cloud backup offers unlimited data protection and application storage with S3 compatibility, ensuring seamless data recovery and privacy compliance, backed by 24/7 support at one-fifth the cost of traditional solutions.
Provides continuous, automated cloud backup and secure, scalable recovery for business servers, endpoints, Microsoft 365, and Google Workspace, protecting critical data from deletion, ransomware, and failure with compliance, threat detection, and easy management features.
Secure cloud backup supporting iPhone, Android, Windows, and more. Featuring quick backups, 256-bit encryption, data protection, and full remote management with file recovery and archiving options.
Open-source, privacy-focused cloud storage using zero-knowledge encryption and blockchain technology, provides secure file transfer, end-to-end encryption, free 10 GB plan, desktop and mobile support, full user control, and no data tracking or ads.
OwnDrive is a security and privacy oriented cloud storage service that gives access to people’s data anywhere, anytime and from any device. OwnDrive makes storing, syncing and sharing of data easy. Our users have the ability to store, sync and share files, contacts, calendars...
Germany
EU
United States
China
Switzerland
Spain
ownCloud can be hosted by someone else, but usually people host it themselves. In the first case, the storage is not unlimited; in the second case it is limited only by the size of the harddisk your server is using. ownCloud does not easily allow "zero-knowledge" encryption, so should be used with Duplicati (backup) or Cryptomator (sync) for results similar to S4.