I built something like this about 13 or so years ago. a startup called contractual.ly - they got acquired by Coupa after I left.
I used the papertrail gem to track changes to the contract object and provided diffs and commenting and then allowing collection of digital signatures (Docusign was pretty new at the time so we rolled our own)
The founder has cofounded another one in the same space https://recitalapp.com/
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