https://github.com/FactomProjectFactom is designed entirely to do this, time-stamping and immutable audit/data trails.
Although its alternative project, it is a data layer designed to be hashed and anchored into the bitcoin blockchain, or the ethereum blockchain.
Check out their whitepaper for more info:
https://www.factom.com/devs/docs/guide/factom-white-paper-1-0Hope you find what you are looking for!