CryptPad is the zero knowledge realtime collaborative editor. Encryption carried out in your web browser protects the data from the server, the cloud and the NSA. This project uses the CKEditor Visual Editor the ChainPad realtime engine and now jQuery.sheet for realtime spreadsheet editing! The secret encryption key is stored in the URL fragment identifier which is never sent to the server but is available to javascript so by sharing the URL, you give authorization to others who want to participate.
CryptPad uses a varient of the Operational transformation algorithm which is able to find distributed consensus using a Nakamoto Blockchain, a construct popularized by Bitcoin. This way the algorithm can avoid the need for a central server to resolve Operational Transform Edit Conflicts and without the need for resolving conflicts, the server can be kept unaware of the content which is being edited on the pad.
NOTE Pads and spreadsheets will be removed after 30 days of inactivity