Stamper is an email-based system that provides secure, digital corroboration of timestamping of messages and documents.
Early in 1995 I was looking for an automatic digital timestamping service which could be used to corroborate the date at which I had signed a document with PGP. At that point I could only find one commercial service and that used proprietary software.
I therefore resolved to setup such a service which would be free of charge to users. I wanted to use PGP as the signing software and provide the service by Internet email, which was at the time by far the most common form of connection to the Internet.