Bit Gold proposal
The Bit Gold proposal, by Nick Szabo, describes a system for the decentralized creation of an unforgeable chain of proofs of work, with each one being attributed to its discoverer, using timestamps and digital signatures. It is said that these proofs of work would have value because they would be scarce and difficult to produce.
It is not said how transfers of ownership would be done. Also, the "strings of bit gold" described cannot be divided.