NoterEth, pronounced "Notaryth", is a prototype notary and "Proof of Existence" DAPP. By submitting hashes of documents you can proof on a later date that you were privileged to certain information at a point in history. The transfer of documents can enable other contracts to allow certain access based on who owns a hash - GitHub 
contract Etherdoc { address owner; function Etherdoc(){ owner = msg.sender; } // In case you sent funds by accident function empty(){ uint256 balance = address(this).balance; address(owner).send(balance); } function newDocument(bytes32 hash) returns (bool success){ if (documentExists(hash)) { success = false; }else{ createHistory(hash, msg.sender, msg.sender); usedHashes[hash] = true; success = true; } return true; } function createHistory (bytes32 hash, address from, address to) internal{ ++latestDocument; documentHashMap[hash] = to; usedHashes[hash] = true; history[latestDocument] = DocumentTransfer(block.number, hash, from, to); DocumentEvent(block.number, hash, from,to); } function transferDocument(bytes32 hash, address recipient) returns (bool success){ success = false; if (documentExists(hash)){ if (documentHashMap[hash] == msg.sender){ createHistory(hash, msg.sender, recipient); success = true; } } return success; } function documentExists(bytes32 hash) constant returns (bool exists){ if (usedHashes[hash]) { exists = true; }else{ exists= false; } return exists; } function getDocument(uint docId) constant returns (uint blockNumber, bytes32 hash, address from, address to){ DocumentTransfer doc = history[docId]; blockNumber = doc.blockNumber; hash = doc.hash; from = doc.from; to = doc.to; } event DocumentEvent(uint blockNumber, bytes32 indexed hash, address indexed from, address indexed to); struct DocumentTransfer { uint blockNumber; bytes32 hash; address from; address to; } function getLatest() constant returns (uint latest){ return latestDocument; } uint latestDocument; mapping(uint => DocumentTransfer) public history; mapping(bytes32 => bool) public usedHashes; mapping(bytes32 => address) public documentHashMap; }