Colored Coins ist sowas ähnliches.
http://www.youtube.com/watch?v=fmFjmvwPGKUWenn man jeden Vertrag in die Blockchain schreibt dann geht die Blockchain Größe ja durch die Decke.
Das könnte man jedoch sicher auch auslagern.
http://www.proofofexistence.com/aboutUse our service to anonymously and securely store an online distributed proof of existence for any document. Your documents are NOT stored in our database or in the Bitcoin blockchain, so you don't have to worry about your data being accessed by others.
All we store is a cryptographic digest of the file, associated to the time in which you uploaded the document. In this way, you can later certify that said data existed at that time. This is the first online service allowing you to publicly prove that you have certain information without revealing the data or yourself, with a decentralized certification based on the Bitcoin network.