SpiderOak provides an private and secure online backup, sync, sharing, access & storage solution for all file and data types. It was designed with a 'Privacy-as-a-Platform' approach. The 'Zero-Knowledge' privacy cloud technology provides a central, private place to store data, free from surveillance by private and public entities. Data is fully encrypted end-to-end (not only during transit) and only the user is able to unlock it using their password. Passwords are never stored by SpiderOak and the company cannot see the names of files or folders in your account.
SpiderOak allows you to securely backup files (including a built-in versioning system), choose to sync data across all of your devices, and share folders or files privately using a password-protected link. Users can have unlimited devices connected to their SpiderOak account which backs up your data so you are able to restore files, even if they are deleted.
Some components of SpiderOak are open source (See GitHub Page). The company intends to be fully open source in the future but as of 2014 their source is not available.
New users get 2GB free (no time limit) and can upgrade to more storage as required.