Not exactly a Bitcoin fork, but the Factom project (factom.org) uses their own data structures and the Bitcoin blockchain to store information in an immutable way.
The user first creates a digital fingerprint of his data that gets into the Factom ledger/blockchain. Then, at regular intervals, the fingerprint of that ledger is published to the Bitcoin blockchain. This way, the amount and complexity of the data that can be much bigger than if that user puts the hash of his information directly on the Bitcoin blockchain, which is limited in size and expensive to publish to.
The project tries to give tools for proof of existence, proof of process and proof of audit.
This couple of videos may give you a good overview of the project:
Factor is Forever: https://www.youtube.com/embed/gVwT-XrrekY
How Does Factom Blockchain Technology Work: https://www.youtube.com/embed/MlzyI1bfyD4