In order to run this you will need MetaMask. This is a very rough product I threw together in a day and I will update it soon, but in the meantime let it server as an example of a quickly built dApp!
Once you clone the repository run:
npm start
Set your MetaMask to use the Kovan Test Network.
See Existence.sol for the smart contract (hosted on Kovan Testnet).
Ethereum Proof of Existence dApp built in a day since I couldn't really find one online!